TLR7 agonists

ABSTRACT

The present invention relates to TLR7 agonists according to Formula I and their use in the treatment of diseases such as cancer and infectious disease.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority of U.S. Provisional ApplicationSer. No. 62/940,622, filed Nov. 26, 2019, which is herein incorporatedin its entirety.

FIELD OF THE INVENTION

The present invention provides TLR7 agonists and prodrugs andpharmaceutical compositions containing them and their use in therapeuticand prophylactic applications. The invention provides methods fortreating and preventing infections, immune disorders, and cancer usingTLR7 agonists.

BACKGROUND OF THE INVENTION

The ultimate goal of cancer immunotherapy is the eradication of tumorcells by the immune system. Both the innate and the adaptive arm of theimmune system can contribute to eradication of tumor cells, with naturalkiller (NK) cells and T cells, respectively, as key players. Crucial inthe adaptive immune response against tumor cells is the activation ofCD8+ cytotoxic T lymphocytes (CTLs), able to exploit their cytotoxicpotential against tumor cells after recognition of tumor-associatedantigens (TAAs). Activation of naïve CD8+ cells occurs viaantigen-presenting cells (APCs), with dendritic cells (DCs) consideredas the most professional APCs. These cells capture and process TAAs,presenting the epitopes at their membrane in complex with majorhistocompatibility complex (MHC) molecules. Maturation of APCs by dangersignals is essential for the presentation of epitopes in a stimulatoryway to T cells.

Peripheral T-cell tolerance against TAAs prevents an effective immuneresponse to tumors, despite the potential of TAA-specific T cells toeliminate tumor cells. The approaches to break this T-cell toleranceagainst TAAs can be divided into two groups: (a) active specificimmunotherapy (also known as cancer vaccines) and (b) passive specificimmunotherapy (by adoptive transfer of antitumor T cells or bymonoclonal antibodies). Poor immunogenicity of tumor cells is also apotential problem in cancer immunotherapy. This low immunogenicity is aresult of the fact that TAAs are mostly self-antigens, and also becauseof the downregulation of human leukocyte antigen and costimulatorymolecules on the membranes of tumor cells. Moreover, tumor cellsactively inhibit the immune system by the secretion of immunosuppressivefactors that interfere with DC and T-cell function.

Toll-like receptors (TLRs) are a class of proteins that play a key rolein the innate immune system. TLRs are a type of pattern recognitionreceptor (PRR) and recognize molecules that are broadly shared bypathogens but distinguishable from host molecules, collectively referredto as pathogen-associated molecular patterns (PAMPs). They are single,membrane-spanning, non-catalytic receptors usually expressed on sentinelcells such as macrophages and dendritic cells, that recognizestructurally conserved molecules derived from microbes.

TLRs 3, 7, 8, and 9 form a group of intracellular TLRs and recognizebacterial or viral nucleic acids. The natural ligand for TLR7 and TLR8is single-stranded RNA that is rich in guanosine and/or uridine. TLR7and TLR8 are also activated by certain small synthetic compounds. Theimidazoquinoline derivates imiquimod (R837) and resiquimod (R848) weredescribed as TLR7 ligands in mice (Hemmi et al., 2002, Nat. Immunol.3:196-200). Additionally, the guanosine analogue loxoribine wasidentified as a TLR7 ligand (Heil et al., 2003, Eur. J. Immunol.33:2987-2997. Additional TLR7 and/or TLR8 ligands include CL097(3M-001), 852A and CL075.

Despite the structural similarities between TLR7 and TLR8, theiractivation has distinct consequences on the innate immune cells andsubsequent production of cytokines. TLR8 agonists are reportedly muchmore effective than TLR7 agonist at inducing pro-inflammatory cytokinesand chemokines, such as tumor necrosis factor (TNF)-α, interleukin(IL)-12, and macrophage inflammatory protein (MIP)-1α, in peripheralblood mononuclear cells (PBMC). In contrast, TLR7 agonists reportedlyactivate plasmacytoid dendritic cells and induced the production ofinterferon (IFN)-α.

After the discovery of the effectiveness of the TLR7/8 agonist imiquimodto protect guinea pigs from herpes virus infection, imiquimod was alsoshown to be effective against several transplantable murine tumors.Clinical responsiveness to topical treatment with imiquimod (Aldara® 5%cream) was reportedly found to be effective for both primary skin tumorsand cutaneous metastases. In these reports, no TAAs were added, and theimmune-enhancing effects of imiquimod were sufficient to elicit anantitumor response. Imiquimod treatment was also reportedly associatedwith partial or total reversal of the aberrant expression of some genesin pre-malignant actinic keratoses, thereby demonstrating the ability ofimiquimod to prevent the development of cancer.

Although treatment with TLR7 agonists in topical cancer show goodanti-cancer effects, it has been challenging to administer theseagonists by oral or systemic routes. In a clinical phase II study inhepatitis C virus infected patients, R848 was administered by the oralroute and showed therapeutic effects on plasma hepatitis virus titers,but with dose-limiting toxicity. In another study, the TLR7 agonist 852Awas tested in a phase II study in patients with metastatic melanoma withthree weekly intravenous doses. The study showed prolonged diseasestabilization in some patients, increased serum IFNα and IP-10, butdose-limiting toxicity in two patients. These studies indicate thatsystemic use of TLR7 agonists in patients may be a challenge due to anarrow therapeutic window.

SUMMARY OF THE INVENTION

The present invention generally relates to compounds useful as TLR7agonists, compositions thereof, methods for their manufacture, andmethods for their use.

In one embodiment the present invention is directed to TLR7 agonistcompounds according to Formula I:

whereinR¹ is independently —H, —OH, —O—C(O)—R⁸ or —F,R² is independently —H, —OH, —O—C(O)—R⁸ or —F,R³ is —OH or —O—C(O)—R⁸,R⁴ is —H, —OH, —O—C(O)—R⁸ or —(C₁-C₈)alkyl,wherein R³ and R⁴ can be in the form of a carbonyl oxygen (═O),R⁵ is —H, —OH, —O—C(O)—R⁸, —(C₁-C₈)alkyl, —O—(C₁-C₈)alkyl, —NH₂ or —NHR⁸wherein R⁴ and R⁵ can form a 3-6 membered cycloalkyl ring,R⁶ is —H, —(C₁-C₅)alkyl, —C(H)═CH₂, —C(H)═CH(C₁-C₈)alkyl),—C(H)═C(C₁-C₈)alkyl)(C₁-C₈)alkyl), —C(H)═C═CH₂, —C(H)═C═C(C₁-C₈)alkyl)H,—CH₂C≡CH, —OH or —O(C₁-C₈)alkyl,R⁷ is —H, —OH, —OCH₃, —SH or —Cl,R⁸ is independently —(C₁-C₈)alkyl, aryl, —(CH₂)_(n)(aryl), heteroaryl or—(CH₂)_(n)(heteroaryl),n is an integer 1, 2, 3, 4 or 5,wherein at least one R⁴ or R⁵ is not —H,wherein each alkyl, cycloalkyl, aryl and heteroaryl are independentlyoptionally substituted by one or more of CN, NO₂, halogen, (C₁-C₃)alkyl,(C₁-C₃)haloalkyl, (C₁-C₃)cycloalkyl, aryl, heteroaryl, OH, alkenyl,alkynyl, O—(C₁-C₃)alkyl, O—C(O)—R⁹, O-(alkylene)aryl,O-(alkylene)heteroaryl, C(O)R⁹, S(C₁-C₈)alkyl, S(O)(C₁-C₈)alkyl,SO₂(C₁-C₈)alkyl, C(O)OR⁹, C(O)NR⁹R⁹, C(O)NR⁹SO₂(C₁-C₈)alkyl, NR⁹R⁹,NR⁹(CO)OR⁹, NH(CO)R⁹, NH(SO₂)(C₁-C₈)alkyl or NH(SO₂)NR⁹R⁹, and R⁹ isindependently —H, —OH, —(C₁-C₈)alkyl, cycloalkyl, heterocyclyl, or thetwo R⁹'s of C(O)NR⁹R⁹ or NR⁹R⁹ combine together with the nitrogen atomto form a heterocycle;or a stereoisomer, a tautomer or a pharmaceutically acceptable saltthereof.

In other embodiments, the TLR7 agonist compound(s) of the invention maybe used alone, or in association with other, further therapeutic agentsand therapeutic procedures, for treating or preventing cancer or aninfection or infectious disease in a subject in need of such treatmentor prevention.

In other embodiments, the present invention provides a pharmaceuticalcomposition comprising (i) a therapeutically effective amount of atleast one compound according to Formula I or a stereoisomer, a tautomeror a pharmaceutically acceptable salt thereof; (ii) in combination witha pharmaceutically acceptable carrier, diluent or excipient.Pharmaceutical compositions comprising a pharmaceutically acceptablecarrier, diluent, or excipient, in association with further therapeuticagents are also part of the present invention.

The above embodiments and other aspects of the invention are readilyapparent in the detailed description that follows. To this end, variousreferences are set forth herein which describe in more detail certainbackground information, procedures, compounds and/or compositions, andare each hereby incorporated by reference in their entireties.

DETAILED DESCRIPTION

The present invention provides compounds as TLR7 agonists. The presentinvention includes TLR7 agonists that activate TLR7 without substantialactivation of TLR8.

Definitions

So that the invention may be more readily understood, certain technicaland scientific terms are specifically defined below. Unless specificallydefined elsewhere in this document, all other technical and scientificterms used herein have the meaning commonly understood by one ofordinary skill in the art to which this invention belongs.

In the following description certain specific details are set forth inorder to provide a thorough understanding of various embodiments of theinvention. However, one skilled in the art will understand that theinvention may be practiced without these details. Unless the contextrequires otherwise, throughout the present specification and claims, theword “comprise” and variations thereof, such as, “comprises” and“comprising” are to be construed in an open, inclusive sense (i.e., as“including, but not limited to”).

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure or characteristicdescribed in connection with the embodiment is included in at least oneembodiment of the present invention. Thus, the appearances of thephrases “in one embodiment” or “in an embodiment” in various placesthroughout this specification are not necessarily all referring to thesame embodiment. Furthermore, the particular features, structures, orcharacteristics may be combined in any suitable manner in one or moreembodiments.

As used herein, including the appended claims, the singular forms ofwords such as “a,” “an,” and “the,” include their corresponding pluralreferences unless the context clearly dictates otherwise.

“Administration” and “treatment,” as it applies to an animal, human,experimental subject, cell, tissue, organ, or biological fluid, refersto contact of an exogenous pharmaceutical, therapeutic, diagnosticagent, or composition to the animal, human, subject, cell, tissue,organ, or biological fluid. Treatment of a cell encompasses contact of areagent to the cell, as well as contact of a reagent to a fluid, wherethe fluid is in contact with the cell. “Administration” and “treatment”also means in vitro and ex vivo treatments, e.g., of a cell, by areagent, diagnostic, binding compound, or by another cell.

“Treat” or “treating” means to administer a therapeutic agent, such as acomposition containing any of the antibodies or antigen-bindingfragments of the present invention, internally or externally to asubject or patient having one or more disease symptoms, or beingsuspected of having a disease, for which the agent has therapeuticactivity. Typically, the therapeutic agent is administered in an amounteffective to alleviate one or more disease symptoms in the treatedsubject or population, whether by inducing the regression of orinhibiting the progression of such symptom(s) by any clinicallymeasurable degree. The amount of a therapeutic agent that is effectiveto alleviate any particular disease symptom may vary according tofactors such as the disease state, age, and weight of the patient, andthe ability of the drug to elicit a desired response in the subject.Whether a disease symptom has been alleviated can be assessed by anyclinical measurement typically used by physicians or other skilledhealthcare providers to assess the severity or progression status ofthat symptom.

“Amino” refers to the —NH₂ substituent.

“Aminocarbonyl” refers to the —C(O)NH₂ substituent.

“Carboxyl” refers to the —CO₂H substituent.

“Carbonyl” refers to a —C(O)— or —C(═O)— group. Both notations are usedinterchangeably within the specification.

“Cyano” refers to the —C≡N substituent.

“Acetyl” refers to the —C(O)CH₃ substituent.

“Hydroxy” or “hydroxyl” refers to the —OH substituent.

“Oxo” refers to a ═O substituent.

“Thio” or “thiol” refer to a —SH substituent.

“Alkyl” refers to a saturated, straight or branched hydrocarbon chainradical consisting solely of carbon and hydrogen atoms, having from oneto twelve carbon atoms (C₁-C₁₂ alkyl), from one to eight carbon atoms(C₁-C₈ alkyl) or from one to six carbon atoms (C₁-C₆ alkyl), and whichis attached to the rest of the molecule by a single bond. Exemplaryalkyl groups include methyl, ethyl, n-propyl, 1-methylethyl(iso-propyl), n-butyl, n-pentyl, 1,1-dimethylethyl (t-butyl),3-methylhexyl, 2-methylhexyl, and the like. Moieties with which thealkyl group can be substituted with are selected from but notnecessarily limited to the group consisting of hydroxyl, amino,alkylamino, arylamino, alkoxy, thioalkoxy, aryloxy, nitro, cyano,sulfonic acid, sulfate, phosphonic acid, phosphate, or phosphonate,either unprotected, or protected as necessary, as known to those skilledin the art, for example, as taught in Greene, et al., “Protective Groupsin Organic Synthesis”, John Wiley and Sons, Second Edition, 1991.

“Lower alkyl” has the same meaning as alkyl defined above but havingfrom one to three carbon atoms (C₁-C₃ alkyl).

“Alkenyl” refers to an unsaturated alkyl group having at least onedouble bond and from two to twelve carbon atoms (C₂-C₁₂ alkenyl), fromtwo to eight carbon atoms (C₂-C₈ alkenyl) or from two to six carbonatoms (C₂-C₆ alkenyl), and which is attached to the rest of the moleculeby a single bond, e.g., ethenyl, propenyl, butenyl, pentenyl, hexenyl,and the like.

“Alkynyl” refers to an unsaturated alkyl group having at least onetriple bond and from two to twelve carbon atoms (C₂-C₁₂ alkynyl), fromtwo to ten carbon atoms (C₂-C₁₀ alkynyl) from two to eight carbon atoms(C₂-C₈ alkynyl) or from two to six carbon atoms (C₂-C₆ alkynyl), andwhich is attached to the rest of the molecule by a single bond, e.g.,ethynyl, propynyl, butynyl, pentynyl, hexynyl, and the like.

“Alkylene” or “alkylene chain” refers to a straight or branched divalenthydrocarbon (alkyl) chain linking the rest of the molecule to a radicalgroup, consisting solely of carbon and hydrogen, respectively. Alkylenescan have from one to twelve carbon atoms, e.g., methylene, ethylene,propylene, n-butylene, and the like. The alkylene chain is attached tothe rest of the molecule through a single or double bond. The points ofattachment of the alkylene chain to the rest of the molecule can bethrough one carbon or any two carbons within the chain. “Optionallysubstituted alkylene” refers to alkylene or substituted alkylene.

“Alkoxy” refers to a radical of the formula —OR_(a) where R_(a) is analkyl having the indicated number of carbon atoms as defined above.Examples of alkoxy groups include without limitation —O-methyl(methoxy), —O-ethyl (ethoxy), —O-propyl (propoxy), —O-isopropyl (isopropoxy) and the like.

“Aryl” refers to a hydrocarbon ring system radical comprising hydrogen,6 to 18 carbon atoms and at least one aromatic ring. Exemplary aryls arehydrocarbon ring system radical comprising hydrogen and 6 to 9 carbonatoms and at least one aromatic ring; hydrocarbon ring system radicalcomprising hydrogen and 9 to 12 carbon atoms and at least one aromaticring; hydrocarbon ring system radical comprising hydrogen and 12 to 15carbon atoms and at least one aromatic ring; or hydrocarbon ring systemradical comprising hydrogen and 15 to 18 carbon atoms and at least onearomatic ring. For purposes of this invention, the aryl radical may be amonocyclic, bicyclic, tricyclic or tetracyclic ring system, which mayinclude fused or bridged ring systems. Aryl radicals include, but arenot limited to, aryl radicals derived from aceanthrylene,acenaphthylene, acephenanthrylene, anthracene, azulene, benzene,chrysene, fluoranthene, fluorene, as-indacene, s-indacene, indane,indene, naphthalene, phenalene, phenanthrene, pleiadene, pyrene, andtriphenylene. “Optionally substituted aryl” refers to an aryl group or asubstituted aryl group. The aryl group can be substituted with, but notnecessarily limited to, one or more moieties selected from the groupconsisting of hydroxyl, amino, alkylamino, arylamino, alkoxy, aryloxy,nitro, cyano, sulfonic acid, sulfate, phosphonic acid, phosphate, orphosphonate, either unprotected, or protected as necessary, as known tothose skilled in the art, for example, as taught in Greene, et al.,“Protective Groups in Organic Synthesis”, John Wiley and Sons, SecondEdition, 1991.

“Cycloalkyl” refers to a stable non-aromatic monocyclic or polycyclichydrocarbon radical consisting solely of carbon and hydrogen atoms,which may include fused or bridged ring systems, having from three tofifteen carbon atoms, preferably having from three to ten carbon atoms,three to nine carbon atoms, three to eight carbon atoms, three to sevencarbon atoms, three to six carbon atoms, three to five carbon atoms, aring with four carbon atoms, or a ring with three carbon atoms. Thecycloalkyl ring may be saturated or unsaturated and attached to the restof the molecule by a single bond. Monocyclic radicals include, forexample, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl,and cyclooctyl. Polycyclic radicals include, for example, adamantyl,norbornyl, decalinyl, 7,7-dimethyl-bicyclo[2.2.1]heptanyl, and the like.

“Fused” refers to any ring structure described herein which is fused toan existing ring structure in the compounds of the invention. When thefused ring is a heterocyclyl ring or a heteroaryl ring, any carbon atomon the existing ring structure which becomes part of the fusedheterocyclyl ring or the fused heteroaryl ring may be replaced with anitrogen atom.

“Halo” or “halogen” refers to bromo (bromine), chloro (chlorine), fluoro(fluorine), or iodo (iodine).

“Haloalkyl” refers to an alkyl radical having the indicated number ofcarbon atoms, as defined herein, wherein one or more hydrogen atoms ofthe alkyl group are substituted with a halogen (halo radicals), asdefined above. The halogen atoms can be the same or different. Exemplaryhaloalkyls are trifluoromethyl, difluoromethyl, trichloromethyl,2,2,2-trifluoroethyl, 1,2-difluoroethyl, 3-bromo-2-fluoropropyl,1,2-dibromoethyl, and the like.

“Heterocyclyl”, heterocycle”, or “heterocyclic ring” refers to a stable3- to 18-membered saturated or unsaturated radical which consists of twoto twelve carbon atoms and from one to six heteroatoms, for example, oneto five heteroatoms, one to four heteroatoms, one to three heteroatoms,or one to two heteroatoms selected from the group consisting ofnitrogen, oxygen and sulfur. Exemplary heterocycles include withoutlimitation stable 3-15 membered saturated or unsaturated radicals,stable 3-12 membered saturated or unsaturated radicals, stable 3-9membered saturated or unsaturated radicals, stable 8-membered saturatedor unsaturated radicals, stable 7-membered saturated or unsaturatedradicals, stable 6-membered saturated or unsaturated radicals, or stable5-membered saturated or unsaturated radicals.

Unless stated otherwise specifically in the specification, theheterocyclyl radical may be a monocyclic, bicyclic, tricyclic ortetracyclic ring system, which may include fused or bridged ringsystems; and the nitrogen, carbon or sulfur atoms in the heterocyclylradical may be optionally oxidized; the nitrogen atom may be optionallyquaternized; and the heterocyclyl radical may be partially or fullysaturated. Examples of non-aromatic heterocyclyl radicals include, butare not limited to, azetidinyl, dioxolanyl, thienyl[1,3]dithianyl,decahydroisoquinolyl, imidazolinyl, imidazolidinyl, isothiazolidinyl,isoxazolidinyl, morpholinyl, octahydroindolyl, octahydroisoindolyl,2-oxopiperazinyl, 2-oxopiperidinyl, 2-oxopyrrolidinyl, oxazolidinyl,piperidinyl, piperazinyl, 4-piperidonyl, pyrrolidinyl, pyrazolidinyl,quinuclidinyl, thiazolidinyl, tetrahydrofuryl, thietanyl, trithianyl,tetrahydropyranyl, thiomorpholinyl, thiamorpholinyl,1-oxo-thiomorpholinyl, and 1,1-dioxo-thiomorpholinyl. Heterocyclylsinclude heteroaryls as defined herein, and examples of aromaticheterocyclyls are listed in the definition of heteroaryls below.

“Heteroaryl” refers to a 5- to 14-membered ring system radicalcomprising hydrogen atoms, one to thirteen carbon atoms, one to sixheteroatoms selected from the group consisting of nitrogen, oxygen andsulfur, and at least one aromatic ring. For purposes of this invention,the heteroaryl radical may be a stable 5-12 membered ring, a stable 5-10membered ring, a stable 5-9 membered ring, a stable 5-8 membered ring, astable 5-7 membered ring, or a stable 6 membered ring that comprises atleast 1 heteroatom, at least 2 heteroatoms, at least 3 heteroatoms, atleast 4 heteroatoms, at least 5 heteroatoms or at least 6 heteroatoms.Heteroaryls may be a monocyclic, bicyclic, tricyclic or tetracyclic ringsystem, which may include fused or bridged ring systems; and thenitrogen, 2 carbon or sulfur atoms in the heteroaryl radical may beoptionally oxidized; the nitrogen atom may be optionally quaternized.The heteroatom may be a member of an aromatic or non-aromatic ring,provided at least one ring in the heteroaryl is aromatic. Examplesinclude, but are not limited to, azepinyl, acridinyl, benzimidazolyl,benzothiazolyl, benzindolyl, benzodioxolyl, benzofuranyl, benzooxazolyl,benzothiazolyl, benzothiadiazolyl, benzo[b][1,4]dioxepinyl,1,4-benzodioxanyl, benzonaphthofuranyl, benzoxazolyl, benzodioxolyl,benzodioxinyl, benzopyranyl, benzopyranonyl, benzofuranyl,benzofuranonyl, benzothienyl (benzothiophenyl), benzotriazolyl,benzo[4,6]imidazo[1,2-a]pyridinyl, carbazolyl, cinnolinyl,dibenzofuranyl, dibenzothiophenyl, furanyl, furanonyl, isothiazolyl,imidazolyl, indazolyl, indolyl, indazolyl, isoindolyl, indolinyl,isoindolinyl, isoquinolyl, indolizinyl, isoxazolyl, naphthyridinyl,oxadiazolyl, 2-oxoazepinyl, oxazolyl, oxiranyl, 1-oxidopyridinyl,1-oxidopyrimidinyl, 1-oxidopyrazinyl, 1-oxidopyridazinyl,1-phenyl-1H-pyrrolyl, phenazinyl, phenothiazinyl, phenoxazinyl,phthalazinyl, pteridinyl, purinyl, pyrrolyl, pyrazolyl, pyridinyl,pyrazinyl, pyrimidinyl, pyridazinyl, quinazolinyl, quinoxalinyl,quinolinyl, quinuclidinyl, isoquinolinyl, tetrahydroquinolinyl,thiazolyl, thiadiazolyl, triazolyl, tetrazolyl, triazinyl, andthiophenyl (i.e. thienyl).

The compounds of the invention may exhibit the phenomenon oftautomerism. While Formula I cannot expressly depict all possibletautomeric forms, it is to be understood that Formula I is intended torepresent any tautomeric form of the depicted compound and not to belimited merely to a specific compound form depicted by the formuladrawing. For example, when R⁷ is OH it is understood for Formula I thatregardless of whether or not the substituents are shown in their enol orketo form as shown below, they represent the same compound. It will beapparent to one skilled in the art, that compounds such as Compound 1:

may exist in such tautomeric forms such as compounds 1A and 1B:

It will also be apparent to one skilled in the art, that compounds witha trifluoromethylketone may also exist in its' corresponding hydrateform.

“Isolated nucleic acid molecule” or “isolated polynucleotide” means aDNA or RNA of genomic, mRNA, cDNA, or synthetic origin or somecombination thereof which is not associated with all or a portion of apolynucleotide in which the isolated polynucleotide is found in nature,or is linked to a polynucleotide to which it is not linked in nature.For purposes of this disclosure, it should be understood that “a nucleicacid molecule comprising” a particular nucleotide sequence does notencompass intact chromosomes. Isolated nucleic acid molecules“comprising” specified nucleic acid sequences may include, in additionto the specified sequences, coding sequences for up to ten or even up totwenty or more other proteins or portions or fragments thereof, or mayinclude operably linked regulatory sequences that control expression ofthe coding region of the recited nucleic acid sequences, and/or mayinclude vector sequences.

The phrase “control sequences” refers to DNA sequences necessary for theexpression of an operably linked coding sequence in a particular hostorganism. The control sequences that are suitable for prokaryotes, forexample, include a promoter, optionally an operator sequence, and aribosome binding site. Eukaryotic cells are known to use promoters,polyadenylation signals, and enhancers.

A nucleic acid or polynucleotide is “operably linked” when it is placedinto a functional relationship with another nucleic acid sequence. Forexample, DNA for a presequence or secretory leader is operably linked toDNA for a polypeptide if it is expressed as a preprotein thatparticipates in the secretion of the polypeptide; a promoter or enhanceris operably linked to a coding sequence if it affects the transcriptionof the sequence; or a ribosome binding site is operably linked to acoding sequence if it is positioned so as to facilitate translation.Generally, but not always, “operably linked” means that the DNAsequences being linked are contiguous, and, in the case of a secretoryleader, contiguous and in reading phase. However, enhancers do not haveto be contiguous. Linking is accomplished by ligation at convenientrestriction sites. If such sites do not exist, the syntheticoligonucleotide adaptors or linkers are used in accordance withconventional practice.

As used herein, the expressions “cell,” “cell line,” and “cell culture”are used interchangeably and all such designations include progeny.Thus, the words “transformants” and “transformed cells” include theprimary subject cell and cultures derived therefrom without regard forthe number of transfers. It is also understood that not all progeny willhave precisely identical DNA content, due to deliberate or inadvertentmutations. Mutant progeny that have the same function or biologicalactivity as screened for in the originally transformed cell areincluded. Where distinct designations are intended, it will be clearfrom the context.

As used herein, “germline sequence” refers to a sequence of unrearrangedimmunoglobulin DNA sequences. Any suitable source of unrearrangedimmunoglobulin sequences may be used. Human germline sequences may beobtained, for example, from JOINSOLVER germline databases on the websitefor the National Institute of Arthritis and Musculoskeletal and SkinDiseases of the United States National Institutes of Health. Mousegermline sequences may be obtained, for example, as described inGiudicelli et al. (2005) Nucleic Acids Res. 33:D256-D261.

The term “in association with” indicates that the componentsadministered in a method of the present invention can be formulated intoa single composition for simultaneous delivery or formulated separatelyinto two or more compositions (e.g., a kit). Each component can beadministered to a subject at a different time than when the othercomponent is administered; for example, each administration may be givennon-simultaneously (e.g., separately or sequentially) at severalintervals over a given period of time. Moreover, the separate componentsmay be administered to a subject by the same or by a different route.

As used herein, the term “effective amount” refer to an amount of a TLR7agonist compound of the invention that, when administered alone or incombination with an additional therapeutic agent to a cell, tissue, orsubject, is effective to cause a measurable improvement in one or moresymptoms of disease, for example cancer or the progression of cancer. Aneffective dose further refers to that amount of a compound orpharmaceutical composition thereof sufficient to result in at leastpartial amelioration of symptoms, e.g., tumor shrinkage or elimination,lack of tumor growth, increased survival time. When applied to anindividual active ingredient administered alone, an effective doserefers to that ingredient alone. When applied to a combination, aneffective dose refers to combined amounts of the active ingredients thatresult in the therapeutic effect, whether administered in combination,serially or simultaneously. An effective amount of a therapeutic willresult in an improvement of a diagnostic measure or parameter by atleast 10%; usually by at least 20%; preferably at least about 30%; morepreferably at least 40%, and most preferably by at least 50%. Aneffective amount can also result in an improvement in a subjectivemeasure in cases where subjective measures are used to assess diseaseseverity.

A “subject” may be a mammal such as a human, dog, cat, horse, cow,mouse, rat, monkey (e.g., cynomolgous monkey, e.g., Macaca fascicularis)or rabbit. In preferred embodiments of the invention, the subject is ahuman subject.

TLR7 Agonists

In one embodiment of Formula I R¹ is —H or —OH.

In an embodiment R¹ is —H.

In an embodiment R² is —H or —OH.

In an embodiment R² is —H

In an embodiment R² is —F.

In an embodiment R³ is —OH or —O—C(O)—CH₃.

In an embodiment R³ is —OH.

In an embodiment R⁴ is —H or —(C₁-C₈)alkyl.

In an embodiment R⁴ is —H or —CH₂CH₃.

In an embodiment R⁵ is —H or —(C₁-C₈)alkyl.

In an embodiment R⁵ is —H or —CH₂CH₃.

In an embodiment R⁶ is —CH₂C≡CH. CH₂CH₂CH₃, or CH₂CH₂CH₂CH₃

In an embodiment R⁶ is —CH₂C≡CH.

In an embodiment R⁷ is —H or —OH.

In an embodiment R⁷ is —OH.

In an embodiment R⁸ is —(C₁-C₈)alkyl.

In an embodiment R⁸ is —CH₃.

General Experimental Methods

Compounds of Formula I can be prepared via the general methods describedbelow.

In one method (Scheme 1), a chlorine atom of the symmetrical4,6-dichloropyrimidine-2,5-diamine [55583-59-0] can be displaced with abenzylic amine such as 4-methoxyl benzyl amine to form II. Exposingintermediate II to phosgene or a phosgene equivalent such as carbonyldiimidazole can form the corresponding cyclic urea III. The chlorineatom of III may be displaced with an appropriate alcohol, preferablybenzylic to form the 2-amino-6, 9-dibenzylic-7,9-dihydro-8H-purin-8-oneIV. The N-7-of purin-8-one IV can be alkylated under basic conditionswith R⁶-Lv to give N-7 alkyl compounds V. R⁶ is a C₁-C₈ alkyl group andLv is defined as a leaving group such as a halogen atom, OSO₂CH₃(mesylate), OSO₂CF₃ (triflate), or OSO₂Ar where Ar is 4-methylphenyl(tosylate). After N-7 alkylation, O-6 and N-9 of V and may bydeprotected under the appropriate conditions. For instance, under acidicconditions such as trifluoroacetic combined with trifluoromethanesulfonic acid, O-6 and N-9 of V are simultaneously removed to give2-amino-7-alkyl-7,9-dihydro-1H-purine-6,8-dione VI. The primary 2-aminogroup may then be protected to form VII where P is a protecting groupsuch as acyl or carbamyl. The synthesis of several furanose sugarintermediates VIII are known in the art and can be derived via multiplesteps from their corresponding carboxaldehydes VIIIa or epoxides VIIIb.In general, purine intermediates VI and VII can then be exposed to asugar derivative VIII under a variety of nucleoside forming reactionconditions, followed by hydroxyl and amine deprotection if required togive 9-β-furano-purine nucleoside analogs of Formula I. For acomprehensive review of the synthetic conditions to form nucleosides seeRomeo, et al., Chem. Rev. 2010, 110, p. 3337-3370.

In another method (Scheme 2) the preparation begins with intermediateIII (described above) where the 6-chlorine purine may behydro-dehalogenated with hydrogen and catalytic Pd or Pt metal or withactivated Zn under acidic conditions to form IX. N-7 alkylation ofintermediate IX can be accomplished under basic conditions with R⁶-Lv togive intermediate X. R⁶ and Lv are defined above in the general methodused in Scheme 1. After N-7 alkylation, N-9 of X and may by deprotectedunder the appropriate conditions. For instance, under acidic conditionssuch as trifluoroacetic combined with trifluoromethane sulfonic acid,the N-9 4-methoxybenzyl group of X is removed to give2-amino-7-alkyl-7,9-dihydro-8H-purin-8-one XI. The primary 2-amino groupof XI may then be protected to form XII where P is a protecting groupsuch as acyl or carbamyl. In general, purine intermediates XI and XIIcan then be exposed to a sugar derivative VIII under a varietynucleoside forming reaction conditions, followed by hydroxyl and aminedeprotection if required to give 9-β-furano-purine nucleoside analogs ofFormula I.

Alternatively, as shown in Scheme 3,2-amino-9-benzylic-7,9-dihydro-8H-purin-8-ones IX can be prepared firstby the hydro-dehalogenation of chloro-pyrimidine II with hydrogen andcatalytic Pd or Pt metal or with activated Zn under acidic conditions toform N⁴-benzylic-2,4,5-triamino-pyrimidines XIII. The imidazolone ringcan then be formed by exposure of XIII to phosgene or a phosgeneequivalent such as carbonyl diimidazole to give intermediate IX.

Using an alternative method (Scheme 4) the synthetic preparation ofcompounds of Formula I may originate from a guanosine nucleoside analogXIV where R¹ and R² can be H, OH, F, R³ is OH, and R⁴ and R⁵ can be H oralkyl. The syntheses of modified sugar guanosine analogs can beaccomplished using procedures described by Zou, et al, Can. J. Chem.,1987, p. 1436 and Robins et al, JOC, 1996, p. 9207. The C-8 of theguanine base can be brominated under conditions described by Holmes, etal., JACS, 1964, p. 1242 and Sheu et al., JACS, 1995, p. 6439 to give an8-bromo-guanosine derivative XV. Oxygen can be introduced at C-8 by theS_(N)Ar displacement of the bromine of XV with an alkoxide of benzylalcohol described by Holmes, et al., JACS, 1965, p. 1772 and Sheu etal., JACS, 1995, p. 6439 to give an 8-benzyloxo-guanosine derivativeXVI. Before debenzylation of the oxygen at C-8 it is necessary toprotect the nitrogen at the N-1 position in order to achieve selectivealkylation of N-7. Broom et al., JOC, 1969, p. 1025 describes theamination of the N-1 of guanosine that in essence acts as a protectinggroup. Thus, intermediate XVI can be exposed to hydroxylamine-O-sulfonicacid under basic conditions to give an N-1 amino-guanosine derivativeXVII. The benzyl group can then be removed from the C-8 oxygen under anumber of de-etherification reaction conditions, preferably viacatalytic hydrogenation with palladium metal to give cyclic ureaintermediate XVIII. N-7 alkylation of intermediate VI can beaccomplished under basic conditions with R⁴-Lv to give an N-7 alkylintermediate XVIII. R⁶ is a C₁-C₈ alkyl group and Lv is defined as aleaving group such as a halogen atom, OSO₂CH₃ (mesylate), OSO₂CF₃(triflate), or OSO₂Ar where Ar is 4-methylphenyl (tosylate). The finalstep in the synthesis is an N-1 deamination of XVIII achieved by forminga diazonium salt with sodium nitrite under aqueous acidic conditions asdescribed in U.S. Pat. No. 5,093,318 to give the desired compounds ofFormula I, where R⁷ is OH.

In another method (Scheme 5) using modified guanosines the amide oxygenof intermediate XVI (described above) can be converted to the 6-chlorinepurine intermediate XX typically with phosphorus oxychloride. The benzylether at C-8 can then selectively be removed by catalytic hydrogenationor with a boron tri-halide such as BCl₃ to give intermediate XXI. N-7alkylation of intermediate XXI can be accomplished under basicconditions with R⁶-Lv to give an N-7 alkyl compounds of Formula I. R⁶and Lv are defined above.

Compounds of Formula I where R⁷ is a chlorine may be further transformedinto other compounds of Formula I where R⁷ is H, OH or OCH₃. To obtaincompounds of Formula I where R⁷ is H, a hydro-dehalogenation reactionmay be utilized. This transformation can usually be conducted underhydrogenation conditions with Pd of Pt or with activated zinc in aceticacid. Displacement of the C-6 chlorine to a hydroxyl group can beaccomplished under aqueous basic or acidic conditions. This chlorine canalso be displaced with methoxide anion to produce compounds of Formula Iwhere R⁷ is OCH₃.

In one other method (Scheme 6) intermediate XVI (described above) isutilized where the amide oxygen can be converted to the 6-thio purineintermediate XXII typically with phosphorus pentasulfide, Lawesson'sreagent or equivalent. The thio group can be reduced with Raney nickelto afford intermediate XXIII. The benzyl ether at C-8 can thenselectively be removed by catalytic hydrogenation or with a borontri-halide such as BCl₃ to give compounds of Formula I. N-7 alkylationunder basic conditions with R⁶-Lv gives compounds of Formula I. R⁶ andLv are defined above.

Therapeutic Uses of TLR7 Agonists

TLR7 activation of innate immunity is principally mediated throughplasmacytoid dendritic cells (pDCs). These cells are the primaryphysiological producers of type I interferons—up to 1,000 times that ofany other cell type. Activation of TLR7 is therefore an important“gatekeeper” to overall induction of the innate immune response. TLR7has significant advantages as a therapeutic target when compared toother TLRs. For example, it can be activated by small molecules whichenables oral administration. Unlike several other TLRs, systemicactivation of TLR7 avoids stimulation of excessive TNF production.

Administration of a TLR7 agonist directly and indirectly engages avariety of anti-tumor mechanisms including: production of cytokines andchemokines that have direct anti-tumor activity; activation of naturalkiller (NK) cells, the primary effector cell of the innate immune systemfor control of cancer, which are then capable of lysing tumor cells byboth antibody-dependent (antibody-dependent cellular cytotoxicity, orADCC) and independent mechanisms; activation of T-cells and reversal ofT-cell exhaustion through antigen presentation by direct cell-cellinteractions with, and production of cytokines and chemokines from pDCs,all leading to increased T-cell mediated attack on tumor cells;increased proliferation and maturation of normal B-cells and theirprecursors, which can enhance endogenous production of antibodies withantitumor activities; and direct activity against aberrant B-cellsthrough the activation of TLR7 on these cells which can induce apoptosisand hypersensitization to chemotherapy.

In one embodiment, the TLR7 agonist compound(s) of the invention may beused alone, or in association with other, further therapeutic agents andtherapeutic procedures, for treating or preventing cancer or aninfection or infectious disease in a subject in need of such treatmentor prevention.

In an embodiment, the TLR7 agonist compound(s) of the invention may beused alone, or in association with tumor vaccines.

In an embodiment, the TLR7 agonist compound(s) of the invention may beused alone, or in association with chemotherapeutic agents.

In an embodiment, the TLR7 agonist compound(s) of the invention may beused alone, or in association with radiation therapy.

In an embodiment, the TLR7 agonist compound(s) of the invention may beused alone, or in association with targeted therapies. Examples oftargeted therapies include: hormone therapies, signal transductioninhibitors (e.g., EGFR inhibitors, such as cetuximab (Erbitux) anderlotinib (Tarceva)); HER2 inhibitors (e.g., trastuzumab (Herceptin) andpertuzumab (Perjeta)); BCR-ABL inhibitors (such as imatinib (Gleevec)and dasatinib (Sprycel)); ALK inhibitors (such as crizotinib (Xalkori)and ceritinib (Zykadia)); BRAF inhibitors (such as vemurafenib(Zelboraf) and dabrafenib (Tafinlar)), gene expression modulators,apoptosis inducers (e.g., bortezomib (Velcade) and carfilzomib(Kyprolis)), angiogenesis inhibitors (e.g., bevacizumab (Avastin) andramucirumab (Cyramza), monoclonal antibodies attached to toxins (e.g.,brentuximab vedotin (Adcetris) and ado-trastuzumab emtansine (Kadcyla)).

In an embodiment, the TLR7 agonist compound(s) of the invention may beused in combination with an anti-cancer therapeutic agent orimmunomodulatory drug such as an immunomodulatory receptor inhibitor oran antibody or antigen-binding fragment thereof that specifically bindsto the receptor.

In an embodiment, the TLR7 agonist compound(s) of the invention may beused in combination with an immune checkpoint inhibitor, an OX40agonist, a 4-1BB agonist, an ICOS agonist, a GITR agonist or anIL2-receptor agonist.

In an embodiment, the TLR7 agonist compound(s) of the invention may beused in combination with an inhibitor or antagonist of PD-1, PD-L1,CTLA4, TIM3, LAG3, SIRPα, CD47, VISTA, BTLA or TIGIT.

In an embodiment, the TLR7 agonist compound(s) of the invention may beused in combination with a therapeutic antibody with anti-tumor activitymediated at least in part through ADCC.

In an embodiment, the TLR7 agonist compound(s) of the invention may beused in combination with a therapeutic antibody with anti-tumor activitymediated at least in part through ADCC, including rituximab, trastuzumaband alemtuzumab.

In an embodiment of the invention, a TLR7 agonist compound of theinvention is in association with an anti-OX40 antibody, includingMOXR0916 and GSK3174998, or other pathway agonist.

In an embodiment of the invention, a TLR7 agonist compound of theinvention is in association with an anti-4-1BB antibody, includingurelumab, utomilumab, or other pathway agonist.

In an embodiment of the invention, a TLR7 agonist compound of theinvention is in association with an anti-ICOS antibody or other pathwayagonist.

In an embodiment of the invention, a TLR7 agonist compound of theinvention is in association with an anti-GITR antibody or other pathwayagonist.

In an embodiment of the invention, a TLR7 agonist compound of theinvention is in association with an IL-2-receptor or other pathwayagonist.

In an embodiment of the invention, a TLR7 agonist compound of theinvention is in association with an anti-PD1 or anti-PDL1 antibody,including nivlumab (Opdivo), pembrolizumab (Keytruda), atezoluzimab(Tecentriq), durvalumab (Imfinzi) or avelumab (Bavencio)).

In an embodiment of the invention, a TLR7 agonist compound of theinvention is in association with a CTLA-4/CD80-CD86 antagonist,including ipilimumab (Yervoy).

In an embodiment of the invention, a TLR7 agonist compound of theinvention is in association with a Tim-3 pathway antagonist, includingMBG453 and TSR-022.

In an embodiment of the invention, a TLR7 agonist compound of theinvention is in association with a LAG-3 pathway antagonist, includingBMS-986016, GSK2831781 and IMP321.

In an embodiment of the invention, a TLR7 agonist compound of theinvention is in association with an anti-SIRPα antibody.

In an embodiment of the invention, a TLR7 agonist compound of theinvention is in association with an anti-CD47 antibody.

In an embodiment of the invention, a TLR7 agonist compound of theinvention is in association with a Vista pathway antagonist.

In an embodiment of the invention, a TLR7 agonist compound of theinvention is in association with a BTLA pathway antagonist.

In an embodiment of the invention, a TLR7 agonist compound of theinvention is in association with a TIGIT pathway antagonist.

In another embodiment, the TLR7 agonist compound(s) of the inventionincrease the activity of an immune cell. The increase of the activity ofan immune cell can be detected using any method known in the art. In oneembodiment, the increase in activity of an immune cell can be detectedby measuring the proliferation of the immune cell. For example, anincrease in activity of a T cell can be detected by measuring theproliferation of the T cell or signal transduction events such astyrosine phosphorylation of immune receptors or downstream kinases thattransmit signals to transcriptional regulators. In other embodiments,the increase in activity of an immune cell can be detected by measuringCTL or NK cell cytotoxic function on specific target cells or IFNγcytokine responses, which are associated with stimulation of anti-tumorimmunity. In yet other embodiments, the increase in activity of animmune cell can be detected by measuring T cell activation ex vivo in asample derived from the subject.

Additional agents which are beneficial to raising a cytolytic T cellresponse may be used in combination with the TLR7 agonist compound ofthe present invention. These include, without limitation, B7costimulatory molecule, interleukin-2 (e.g., NKTR-214), interferon-7,GM-CSF, CTLA-4 antagonists, OX-40/OX-40 ligand, CD40/CD40 ligand,sargramostim, levamisol, vaccinia virus, Bacille Calmette-Guerin (BCG),liposomes, alum, Freund's complete or incomplete adjuvant, detoxifiedendotoxins, mineral oils, surface active substances such aslipolecithin, pluronic polyols, polyanions, peptides, and oil orhydrocarbon emulsions.

In an embodiment of the invention, a TLR7 agonist compound of theinvention is in association with one or more antiemetics including, butnot limited to: casopitant (GlaxoSmithKline), Netupitant (MGI-Helsinn)and other NK-1 receptor antagonists, palonosetron (sold as Aloxi by MGIPharma), aprepitant (sold as Emend by Merck and Co.; Rahway, N.J.),diphenhydramine (sold as Benadryl® by Pfizer; New York, N.Y.),hydroxyzine (sold as Atarax® by Pfizer; New York, N.Y.), metoclopramide(sold as Reglan® by AH Robins Co; Richmond, Va.), lorazepam (sold asAtivan® by Wyeth; Madison, N.J.), alprazolam (sold as Xanax® by Pfizer;New York, N.Y.), haloperidol (sold as Haldol® by Ortho-McNeil; Raritan,N.J.), droperidol (Inapsine®), dronabinol (sold as Marinol® by SolvayPharmaceuticals, Inc.; Marietta, Ga.), dexamethasone (sold as Decadron®by Merck and Co.; Rahway, N.J.), methylprednisolone (sold as Medrol® byPfizer; New York, N.Y.), prochlorperazine (sold as Compazine® byGlaxosmithkline; Research Triangle Park, NC), granisetron (sold asKytril® by Hoffmann-La Roche Inc.; Nutley, N.J.), ondansetron (sold asZofran® by Glaxosmithkline; Research Triangle Park, NC), dolasetron(sold as Anzemet® by Sanofi-Aventis; New York, N.Y.), tropisetron (soldas Navoban® by Novartis; East Hanover, N.J.).

Other side effects of cancer treatment include red and white blood celldeficiency. Accordingly, in an embodiment of the invention, a TLR7agonist compound is in association with an agent which treats orprevents such a deficiency, including filgrastim, PEG-filgrastim,erythropoietin, epoetin alfa and darbepoetin alfa.

In another embodiment, the present invention relates to compositionscomprising one or more TLR7 agonist compounds of the present inventionand a pharmaceutically acceptable carrier or diluent. Such compositionscan further comprise one or more other therapeutically activeingredients such as an agonistic antibody or antigen-binding fragmentthereof, or a soluble fusion, of a TNF receptor protein, animmunoglobulin-like protein, a cytokine receptor, an integrin, asignaling lymphocytic activation molecules (SLAM proteins), OX40, 4-1BB(CD137), ICOS (CD278), GITR, IL2R beta (CD122) and/or IL2R gamma.

The present invention includes compositions comprising a TLR7 agonistcompound of the present invention in association with one or moreantibodies that target the PD-1/PD-L1 interaction or CTLA-4/CD80-CD86interaction. Non-limiting examples of such antibodies includepembrolizumab, nivolumab, avelumab, REGN2810, MEDI-0680, PDR-001,SHR-1210, BGB-A317, PF-06801591, TSR-042, atezoluzimab, durvalumab,BMS-936559, ipilimumab and tremelimumab.

Compositions for inducing a T cell immune response which preferentiallystimulate a cytolytic T cell response versus an antibody response arepreferred, although those that stimulate both types of response can beused as well.

In another embodiment compositions comprising one or more TLR7 agonistcompounds can further comprise one or more other therapeutically activeingredients that are an immune checkpoint inhibitor, an OX40 agonist, a4-1BB agonist, an ICOS agonist, a GITR agonist or an IL2-receptoragonist.

In another embodiment compositions comprising one or more TLR7 agonistcompounds can further comprise one or more other therapeutically activeingredients that are an inhibitor or antagonist of PD-1, PD-L1, CTLA4,TIM3, LAG3, SIRPα, CD47, VISTA, BTLA or TIGIT.

In another embodiment compositions comprising one or more TLR7 agonistcompounds can further comprise one or more other therapeutically activeingredients that are a therapeutic antibody with anti-tumor activitymediated at least in part through ADCC.

In another embodiment compositions comprising one or more TLR7 agonistcompounds can further comprise one or more other therapeutically activeingredients that are a therapeutic antibody with anti-tumor activitymediated at least in part through ADCC, including rituximab, trastuzumaband alemtuzumab.

Further provided in the invention are methods for treating or preventingcancer or an infection or infectious disease in a subject in need ofsuch treatment or prevention, in subjects, including human subjects,with the TLR7 agonist compound(s) disclosed herein. In one embodiment ofthe invention, such subject suffers from cancer or a precancerouscondition. In another embodiment of the invention, such subject suffersfrom an infection or an infectious disease.

In another embodiment the present invention also relates to methods oftreating or preventing cancer in a human subject, comprisingadministering to the subject an effective amount of one or more TLR7agonist compounds of the present invention, optionally in associationwith a further therapeutic agent or therapeutic procedure; and tomethods of treating an infection or infectious disease in a humansubject, comprising administering to the subject an effective amount ofone or more TLR7 agonist compounds of the present invention, optionallyin association with a further therapeutic agent or therapeuticprocedure.

In yet another embodiment the present invention relates to a method ofincreasing the activity of an immune cell, comprising administering to asubject in need thereof an effective amount of one or more TLR7 agonistcompounds of the present invention for treating or preventing cancer;treating an infection or infectious disease; acting as a vaccineadjuvant; or increasing immune cell activation.

In an embodiment, the invention provides methods for treating subjectsusing a TLR7 agonist compound of the invention, wherein the subjectsuffers from cancer or a precancerous condition. In an embodiment thecancer is, e.g., osteosarcoma, rhabdomyosarcoma, neuroblastoma, kidneycancer, leukemia, renal transitional cell cancer, bladder cancer, Wilm'scancer, ovarian cancer, pancreatic cancer, breast cancer, prostatecancer, bone cancer, lung cancer (e.g., non-small cell lung cancer),gastric cancer, colorectal cancer, cervical cancer, synovial sarcoma,head and neck cancer, squamous cell carcinoma, multiple myeloma, renalcell cancer, retinoblastoma, hepatoblastoma, hepatocellular carcinoma,melanoma, rhabdoid tumor of the kidney, Ewing's sarcoma, chondrosarcoma,brain cancer, glioblastoma, meningioma, pituitary adenoma, vestibularschwannoma, a primitive neuroectodermal tumor, medulloblastoma,astrocytoma, anaplastic astrocytoma, oligodendroglioma, ependymoma,choroid plexus papilloma, polycythemia vera, thrombocythemia, idiopathicmyelfibrosis, soft tissue sarcoma, thyroid cancer, endometrial cancer,carcinoid cancer or liver cancer, breast cancer or gastric cancer. In anembodiment of the invention, the cancer is metastatic cancer, e.g., ofthe varieties described above.

In an embodiment, the invention provides methods for treating orpreventing viral infections in a subject using a TLR7 agonist of FormulaI. In one embodiment, the viral infection is infection with a virusselected from the group consisting of human immunodeficiency virus(HIV), hepatitis virus (A, B, C, or D), herpes virus (e.g., VZV, HSV-I,HAV-6, HSV-II, and CMV, Epstein Barr virus), adenovirus, influenzavirus, flaviviruses, echovirus, rhinovirus, coxsackie virus, coronavirus(e.g., SARS-CoV, MERS, and SARS-CoV-2), respiratory syncytial virus,mumps virus, rotavirus, measles virus, rubella virus, parvovirus,vaccinia virus, HTLV virus, dengue virus, papillomavirus, molluscumvirus, poliovirus, rabies virus, JC virus, arboviral encephalitis virus.

The present invention includes methods for treating and preventing viralinfections in a subject comprising administering an effective amount ofthe TLR7 agonist compound of Formula I and one or more additionaltreatment modalities (e.g. small-molecule therapeutic agents, protein orpeptide therapeutics, antibodies, sera from persons that have recoveredfrom viral infections, and therapeutic or preventative vaccines).

In an embodiment, the invention provides methods for treating subjectsusing a TLR7 agonist compound of the invention, wherein the subjectsuffers from a bacterial infection. In one embodiment, the bacterialinfection is infection with a bacterium selected from the groupconsisting of Chlamydia, rickettsial bacteria, mycobacteria,staphylococci, streptococci, pneumonococci, meningococci and gonococci,klebsiella, proteus, serratia, pseudomonas, Legionella, Corynebacteriumdiphtheriae, Salmonella, bacilli, Vibrio cholerae, Clostridium tetan,Clostridium botulinum, Bacillus anthricis, Yersinia pestis,Mycobacterium leprae, Mycobacterium lepromatosis, and Borriella.

In an embodiment, the invention provides methods for treating subjectsusing a TLR7 agonist compound of the invention, wherein the subjectsuffers from a fungal infection. In one embodiment, the fungal infectionis infection with a fungus selected from the group consisting of Candida(albicans, krusei, glabrata, tropicalis, etc.), Cryptococcus neoformans,Aspergillus (fumigatus, niger, etc.), Genus Mucorales (mucor, absidia,rhizopus), Sporothrix schenkii, Blastomyces dermatitidis,Paracoccidioides brasiliensis, Coccidioides immitis and Histoplasmacapsulatum.

In an embodiment, the invention provides methods for treating subjectsusing a TLR7 agonist compound of the invention, wherein the subjectsuffers from a parasitic infection. In one embodiment, the parasiticinfection is infection with a parasite selected from the groupconsisting of Entamoeba histolytica, Balantidium coi, Naegleria fowleri,Acanthamoeba, Giardia lambia, Cryptosporidium, Pneumocystis carinii,Plasmodium vivax, Babesia microti, Trypanosoma brucei, Trypanosomacruzi, Leishmania donovani, Toxoplasma gondii and Nippostrongylusbrasiliensis.

The present invention includes methods for treating or preventing cancerin a subject comprising administering an effective amount of the TLR7agonist compound of the present invention and one or more antibodiesthat target the PD-1/PD-L1 or CTLA-4/CD80-CD86 interaction to thesubject. In an embodiment of the invention, a TLR7 agonist compound ofthe invention is in association with an anti-PD1 or anti-PDL1 antibody.

The present invention includes methods for treating or preventing cancerin a subject comprising administering an effective amount of the TLR7agonist compound of the present invention in combination with an immunecheckpoint inhibitor, an OX40 agonist, a 4-1BB agonist, an ICOS agonist,a GITR agonist or an IL2-receptor agonist.

The present invention includes methods for treating or preventing cancerin a subject comprising administering an effective amount of the TLR7agonist compound of the present invention in combination with aninhibitor or antagonist of PD-1, PD-L1, CTLA4, TIM3, LAG3, SIRPα, CD47,VISTA, BTLA or TIGIT.

The present invention includes methods for treating or preventing cancerin a subject comprising administering an effective amount of the TLR7agonist compound of the present invention in combination with atherapeutic antibody with anti-tumor activity mediated at least in partthrough ADCC.

The present invention includes methods for treating or preventing cancerin a subject comprising administering an effective amount of the TLR7agonist compound of the present invention in combination with atherapeutic antibody with anti-tumor activity mediated at least in partthrough ADCC, including rituximab, trastuzumab and alemtuzumab.

The present invention includes methods for treating or preventing cancerin a subject comprising administering an effective amount of the TLR7agonist compound of the present invention in association with ananti-OX40 antibody, including MOXR0916 and GSK3174998, or other pathwayagonist.

The present invention includes methods for treating or preventing cancerin a subject comprising administering an effective amount of the TLR7agonist compound of the present invention in association with ananti-4-1BB antibody, including urelumab, utomilumab, or other pathwayagonist.

The present invention includes methods for treating or preventing cancerin a subject comprising administering an effective amount of the TLR7agonist compound of the present invention in association with ananti-ICOS antibody or other pathway agonist.

The present invention includes methods for treating or preventing cancerin a subject comprising administering an effective amount of the TLR7agonist compound of the present invention in association with ananti-GITR antibody or other pathway agonist.

The present invention includes methods for treating or preventing cancerin a subject comprising administering an effective amount of the TLR7agonist compound of the present invention in association with anIL-2-receptor or other pathway agonist.

The present invention includes methods for treating or preventing cancerin a subject comprising administering an effective amount of the TLR7agonist compound of the present invention in association with ananti-PD1 or anti-PDL1 antibody, including nivlumab (Opdivo),pembrolizumab (Keytruda), atezoluzimab (Tecentriq), durvalumab (Imfinzi)or avelumab (Bavencio)).

The present invention includes methods for treating or preventing cancerin a subject comprising administering an effective amount of the TLR7agonist compound of the present invention in association with aCTLA-4/CD80-CD86 antagonist, including ipilimumab (Yervoy).

The present invention includes methods for treating or preventing cancerin a subject comprising administering an effective amount of the TLR7agonist compound of the present invention in association with a Tim-3pathway antagonist, including MBG453 and TSR-022.

The present invention includes methods for treating or preventing cancerin a subject comprising administering an effective amount of the TLR7agonist compound of the present invention in association with a LAG-3pathway antagonist, including BMS-986016, GSK2831781 and IMP321.

The present invention includes methods for treating or preventing cancerin a subject comprising administering an effective amount of the TLR7agonist compound of the present invention in association with ananti-SIRPα antibody.

The present invention includes methods for treating or preventing cancerin a subject comprising administering an effective amount of the TLR7agonist compound of the present invention in association with ananti-CD47 antibody.

The present invention includes methods for treating or preventing cancerin a subject comprising administering an effective amount of the TLR7agonist compound of the present invention in association with a Vistapathway antagonist.

The present invention includes methods for treating or preventing cancerin a subject comprising administering an effective amount of the TLR7agonist compound of the present invention in association with a BTLApathway antagonist.

The present invention includes methods for treating or preventing cancerin a subject comprising administering an effective amount of the TLR7agonist compound of the present invention in association with a TIGITpathway antagonist.

Pharmaceutical Compositions and Administration

The present invention also provides a pharmaceutical compositioncomprising (i) a therapeutically effective amount of at least onecompound according to Formula I or a stereoisomer, a tautomer or apharmaceutically acceptable salt thereof; (ii) in combination with apharmaceutically acceptable carrier, diluent or excipient.Pharmaceutical compositions comprising a pharmaceutically acceptablecarrier, diluent, or excipient, in association with further therapeuticagents are also part of the present invention.

The term “pharmaceutical” as used herein refers to a chemical substanceintended for use in the cure, treatment, or prevention of disease andwhich is subject to an approval process by the U.S. Food and DrugAdministration (or a non-U.S. equivalent thereof) as a prescription orover-the-counter drug product. Details on techniques for formulation andadministration of such compositions may be found in Remington, TheScience and Practice of Pharmacy 21^(st) Edition (Mack Publishing Co.,Easton, Pa.) and Nielloud and Marti-Mestres, Pharmaceutical Emulsionsand Suspensions: 2^(nd) Edition (Marcel Dekker, Inc, New York). Toprepare pharmaceutical or sterile compositions of the TLR7 agonistcompound(s) of the invention, the compound(s) is(are) admixed with apharmaceutically acceptable carrier or excipient. See, e.g., Remington'sPharmaceutical Sciences and U.S. Pharmacopeia: National Formulary, MackPublishing Company, Easton, Pa. (1984).

Formulations of therapeutic and diagnostic agents may be prepared bymixing with acceptable carriers, excipients, or stabilizers in the formof, e.g., lyophilized powders, slurries, aqueous solutions orsuspensions (see, e.g., Hardman, et al. (2001) Goodman and Gilman's ThePharmacological Basis of Therapeutics, McGraw-Hill, New York, N.Y.;Gennaro (2000) Remington: The Science and Practice of Pharmacy,Lippincott, Williams, and Wilkins, New York, N.Y.; Avis, et al. (eds.)(1993) Pharmaceutical Dosage Forms: Parenteral Medications, MarcelDekker, NY; Lieberman, et al. (eds.) (1990) Pharmaceutical Dosage Forms:Tablets, Marcel Dekker, NY; Lieberman, et al. (eds.) (1990)Pharmaceutical Dosage Forms: Disperse Systems, Marcel Dekker, NY; Weinerand Kotkoskie (2000) Excipient Toxicity and Safety, Marcel Dekker, Inc.,New York, N.Y.).

Toxicity and therapeutic efficacy of the compounds or compositions ofthe invention, administered alone or in combination with anothertherapeutic agent, can be determined by standard pharmaceuticalprocedures in cell cultures or experimental animals, e.g., fordetermining the LD₅₀ (the dose lethal to 50% of the population) and theED₅₀ (the dose therapeutically effective in 50% of the population). Thedose ratio between toxic and therapeutic effects is the therapeuticindex (LD₅₀/ED₅₀). The data obtained from these cell culture assays andanimal studies can be used in formulating a range of dosage for use inhuman. The dosage of such compounds lies preferably within a range ofcirculating concentrations that include the ED₅₀ with little or notoxicity. The dosage may vary within this range depending upon thedosage form employed and the route of administration.

In a further embodiment, a further therapeutic agent that isadministered to a subject in association with a TLR7 agonist compound ofthe invention in accordance with the Physicians' Desk Reference 2003(Thomson Healthcare; 57th edition (Nov. 1, 2002)).

The mode of administration can vary. For the purposes of thisdisclosure, the pharmaceutical compositions may be administered by avariety of means including non-parenterally, parenterally, by inhalationspray, topically, or rectally in formulations containingpharmaceutically acceptable carriers, adjuvants and vehicles.“Non-parenteral administration” encompasses oral, buccal, sublingual,topical, transdermal, ophthalmic, otic, nasal, rectal, cervical,pulmonary, mucosal, and vaginal routes. The term parenteral as used hereincludes but is not limited to subcutaneous, intravenous, intramuscular,intraarterial, intradermal, intrathecal and epidural injections with avariety of infusion techniques. Intraarterial and intravenous injectionas used herein includes administration through catheters. Intra-tumoral(directly into the tumor mass) or peri-tumoral (around the tumor mass)administration of the compound(s) of the present invention are alsocontemplated. The term oral as used herein includes, but is not limitedto oral ingestion, or delivery by a sublingual or buccal route. Oraladministration includes fluid drinks, energy bars, as well as pillformulations.

Pharmaceutical compositions may be in any form suitable for the intendedmethod of administration. When used for oral use for example, tablets,troches, lozenges, aqueous or oil suspensions, dispersible powders orgranules, emulsions, hard or soft capsules, syrups or elixirs may beprepared. Compositions intended for oral use may be prepared accordingto any method known to the art for the manufacture of pharmaceuticalcompositions and such compositions may contain one or more agentsincluding sweetening agents, flavoring agents, coloring agents andpreserving agents, in order to provide a palatable preparation. Tabletscontaining a drug compound in admixture with non-toxic pharmaceuticallyacceptable excipient which are suitable for manufacture of tablets areacceptable. These excipients may be, for example, inert diluents, suchas calcium or sodium carbonate, lactose, calcium or sodium phosphate;granulating and disintegrating agents, such as maize starch, or alginicacid; binding agents, such as starch, gelatin or acacia; and lubricatingagents; such as magnesium stearate, stearic acid or talc. Tablets may beuncoated, or may be coated by known techniques including entericcoating, colonic coating, or microencapsulation to delay disintegrationand adsorption in the gastrointestinal tract and/or provide a sustainedaction over a longer period. For example, a time delay material such asglyceryl monostearate or glyceryl distearate alone or with a wax may beemployed.

The present invention provides a vessel (e.g., a plastic or glass vial,e.g., with a cap or a chromatography column, hollow bore needle or asyringe cylinder) comprising one or more compounds of the invention or apharmaceutical composition thereof. The present invention also providesan injection device comprising one or more compounds of the invention ora pharmaceutical composition thereof. An injection device is a devicethat introduces a substance into the body of a patient via a parenteralroute, e.g., intramuscular, subcutaneous or intravenous. For example, aninjection device may be a syringe (e.g., pre-filled with thepharmaceutical composition, such as an auto-injector) which, forexample, includes a cylinder or barrel for holding fluid to be injected(e.g., one or more compounds of the invention or a pharmaceuticalcomposition thereof), a needle for piecing skin and/or blood vessels forinjection of the fluid; and a plunger for pushing the fluid out of thecylinder and through the needle bore. In an embodiment of the invention,an injection device that comprises one or more compounds of theinvention or a pharmaceutical composition thereof is an intravenous (IV)injection device. Such a device includes one or more compounds of theinvention or a pharmaceutical composition thereof in a cannula ortrocar/needle which may be attached to a tube which may be attached to abag or reservoir for holding fluid (e.g., saline; or lactated ringersolution comprising NaCl, sodium lactate, KCl, CaCl₂) and optionallyincluding glucose) introduced into the body of the patient through thecannula or trocar/needle. The one or more compounds of the invention ora pharmaceutical composition thereof may, in an embodiment of theinvention, be introduced into the device once the trocar and cannula areinserted into the vein of a subject and the trocar is removed from theinserted cannula. The IV device may, for example, be inserted into aperipheral vein (e.g., in the hand or arm); the superior vena cava orinferior vena cava, or within the right atrium of the heart (e.g., acentral IV); or into a subclavian, internal jugular, or a femoral veinand, for example, advanced toward the heart until it reaches thesuperior vena cava or right atrium (e.g., a central venous line). In anembodiment of the invention, an injection device is an autoinjector; ajet injector or an external infusion pump. A jet injector uses ahigh-pressure narrow jet of liquid which penetrate the epidermis tointroduce the one or more compounds of the invention or a pharmaceuticalcomposition thereof to a patient's body. External infusion pumps aremedical devices that deliver a pharmaceutical composition into apatient's body in controlled amounts. External infusion pumps may bepowered electrically or mechanically. Different pumps operate indifferent ways, for example, a syringe pump holds fluid in the reservoirof a syringe, and a moveable piston controls fluid delivery, anelastomeric pump holds fluid in a stretchable balloon reservoir, andpressure from the elastic walls of the balloon drives fluid delivery. Ina peristaltic pump, a set of rollers pinches down on a length offlexible tubing, pushing fluid forward. In a multi-channel pump, fluidscan be delivered from multiple reservoirs at multiple rates.

The compounds and pharmaceutical compositions disclosed herein may alsobe administered with a needleless hypodermic injection device; such asthe devices disclosed in U.S. Pat. Nos. 6,620,135; 6,096,002; 5,399,163;5,383,851; 5,312,335; 5,064,413; 4,941,880; 4,790,824 or 4,596,556. Suchneedleless devices comprising the pharmaceutical composition are alsopart of the present invention. The pharmaceutical compositions disclosedherein may also be administered by infusion. Examples of well-knownimplants and modules for administering the pharmaceutical compositionsinclude those disclosed in: U.S. Pat. No. 4,487,603, which discloses animplantable micro-infusion pump for dispensing medication at acontrolled rate; U.S. Pat. No. 4,447,233, which discloses a medicationinfusion pump for delivering medication at a precise infusion rate; U.S.Pat. No. 4,447,224, which discloses a variable flow implantable infusionapparatus for continuous drug delivery; U.S. Pat. No. 4,439,196, whichdiscloses an osmotic drug delivery system having multi-chambercompartments. Many other such implants, delivery systems, and modulesare well known to those skilled in the art and those comprising thepharmaceutical compositions of the present invention are within thescope of the present invention.

Alternately, one may administer the TLR7 agonist compound of theinvention in a local rather than systemic manner, for example, viainjection of the compound into a tumor. Furthermore, one may administerthe TLR7 agonist compound of the invention in a targeted drug deliverysystem, for example, in a liposome coated with a tissue-specificantibody, targeting, for example, a tumor characterized byimmunopathology. The liposomes will be targeted to and taken upselectively by the corresponding tissue. Such methods and liposomes arepart of the present invention.

When a disclosed compound or its salt is named or depicted by structure,it is to be understood that the compound or salt, including solvates(particularly, hydrates) thereof, may exist in crystalline forms,non-crystalline forms or a mixture thereof. The compound or salt, orsolvates (particularly, hydrates) thereof, may also exhibit polymorphism(i.e., the capacity to occur in different crystalline forms). Thesedifferent crystalline forms are typically known as “polymorphs.” It isto be understood that when named or depicted by structure, the disclosedcompound, or solvates (particularly, hydrates) thereof, also include allpolymorphs thereof. Polymorphs have the same chemical composition butdiffer in packing, geometrical arrangement, and other descriptiveproperties of the crystalline solid state. Polymorphs may have differentphysical properties such as density, shape, hardness, stability, anddissolution properties. Polymorphs typically exhibit different meltingpoints, IR spectra, and X-ray powder diffraction patterns, which may beused for identification. One of ordinary skill in the art willappreciate that different polymorphs may be produced, for example, bychanging or adjust the conditions used during the crystallization orrecrystallization of the compound.

For solvates of compounds of this invention, or salts thereof, that arein crystalline form, the skilled artisan will appreciate thatpharmaceutically acceptable solvates may be formed wherein solventmolecules are incorporated into the crystalline lattice duringcrystallization. Solvates may involve nonaqueous solvents such asethanol, isopropanol, dimethyl sulfoxide, acetic acid, ethanolamine, andethyl acetate, or they may involve water as the solvent that isincorporated into the crystalline lattice. Solvates wherein water is thesolvent that is incorporated into the crystalline lattice are typicallyreferred to as “hydrates.” Hydrates include stoichiometric hydrates aswell as compositions containing variable amounts of water. The inventionincludes all such solvates.

Because of their potential use in medicine, the salts of the compound(s)of the invention are preferably pharmaceutically acceptable. Suitablepharmaceutically acceptable salts include those described by P. HeinrichStahl and Camille G. Wermuth in Handbook of Pharmaceutical Salts:Properties, Selection, and Use, 2^(nd) ed. (Wiley-VCH: 2011) and alsoRemington's Pharmaceutical Sciences, 18^(th) ed. (Mack Publishing,Easton Pa.: 1990) and also Remington: The Science and Practice ofPharmacy, 19^(th) ed. (Mack Publishing, Easton Pa.: 1995).

Representative pharmaceutically acceptable salts include, e.g., alkalimetal salts, alkali earth salts, ammonium salts, water-soluble andwater-insoluble salts, such as the acetate, amsonate(4,4-diaminostilbene-2,2-disulfonate), benzenesulfonate, benzonate,bicarbonate, bisulfate, bitartrate, borate, bromide, butyrate, calcium,calcium edetate, camsylate, carbonate, chloride, citrate, clavulariate,dihydrochloride, edetate, edisylate, estolate, esylate, fiunarate,gluceptate, gluconate, glutamate, glycollylarsanilate,hexafluorophosphate, hexylresorcinate, hydrabamine, hydrobromide,hydrochloride, hydroxynaphthoate, iodide, isothionate, lactate,lactobionate, laurate, malate, maleate, mandelate, mesylate,methylbromide, methylnitrate, methylsulfate, mucate, napsylate, nitrate,N-methylglucamine ammonium salt, 3-hydroxy-2-naphthoate, oleate,oxalate, palmitate, pamoate (1,1-methene-bis-2-hydroxy-3-naphthoate,einbonate), pantothenate, phosphate/diphosphate, picrate,polygalacturonate, propionate, p-toluenesulfonate, salicylate, stearate,subacetate, succinate, sulfate, sulfosaliculate, suramate, tannate,tartrate, teoclate, tosylate, triethiodide, trifluoroacetate, andvalerate salts. A pharmaceutically acceptable salt can have more thanone charged atom in its structure. In this instance the pharmaceuticallyacceptable salt can have multiple counterions. Thus, a pharmaceuticallyacceptable salt can have one or more charged atoms and/or one or morecounterions.

Salts of a compound of the present invention may be prepared by anysuitable method known in the art, including treatment of the free baseswith an inorganic acid, such as hydrochloric acid, hydrobromic acid,sulfuric acid, nitric acid, phosphoric acid, and the like, or with anorganic acid, such as acetic acid, trifluoroacetic acid, maleic acid,succinic acid, mandelic acid, fumaric acid, malonic acid, formic acid,alginic acid, pyruvic acid, oxalic acid, glycolic acid, salicylic acid,pyranosildyl acid, such as glucuronic acid or galacturonic acid,alphahydroxy acid, such as citric acid or tartaric acid, amino acid,such as aspartic acid or glutamic acid, aromatic acid, such as benzoicacid or cinnamic acid, sulfonic acid, such as p-toluenesulfonic acid,methanesulfonic acid, ethanesulfonic acid or the like.

A pharmaceutically acceptable salt may be made with a base which affordsa pharmaceutically acceptable cation, which includes alkali metal salts(especially sodium and potassium), alkaline earth metal salts(especially calcium and magnesium), aluminum salts and ammonium salts,zinc, as well as salts made from physiologically acceptable organicbases such as diethylamine, isopropylamine, olamine, benzathine,benethamine, tromethamine (2-amino-2-(hydroxymethyl)propane-1,3-diol),morpholine, epolamine, piperidine, piperazine, picoline,dicyclohexylamine, N,N′-dibenzylethylenediamine, 2-hydroxyethylamine,tri-(2-hydroxyethyl)amine, chloroprocaine, choline, deanol, imidazole,diethanolamine, ethylenediamine, meglumine (N-methylglucamine),procaine, dibenzylpiperidine, dehydroabietylamine, glucamine, collidine,quinine, quinolone, erbumine and basic amino acids such as lysine andarginine.

If a compound containing a basic amine or other basic functional groupis isolated as a salt, the corresponding free base form of that compoundmay be prepared by any suitable method known to the art, includingtreatment of the salt with an inorganic or organic base, suitably aninorganic or organic base having a higher pK_(a) than the free base formof the compound. Similarly, if a compound containing a phosphatediester, phosphorothioate diester or other acidic functional group isisolated as a salt, the corresponding free acid form of that compoundmay be prepared by any suitable method known to the art, includingtreatment of the salt with an inorganic or organic acid, suitably aninorganic or organic acid having a lower pK_(a) than the free acid formof the compound.

An effective amount of a compound or a pharmaceutically acceptable salt,pharmaceutically acceptable solvate or pharmaceutically acceptablehydrate thereof, as described herein, for a particular patient may varydepending on factors such as the condition being treated, the overallhealth of the patient, the route and dose of administration and theseverity of side effects.

“A pharmaceutically acceptable prodrug” is a compound that may beconverted under physiological conditions or by solvolysis to thespecified compound or to a pharmaceutically acceptable salt of suchcompound prior to exhibiting its pharmacological effect(s). Typically,the prodrug is formulated with the objective(s) of improved chemicalstability, improved patient acceptance and compliance, improvedbioavailability, prolonged duration of action, improved organselectivity, improved formulation (e.g., increased hydrosolubility),and/or decreased side effects (e.g., toxicity). The prodrug can bereadily prepared from the compounds of Formula I using methods known inthe art, such as those described by Burger's Medicinal Chemistry andDrug Chemistry. 1, 172-178, 949-982 (1995.) See also Bertolini et al.,J. Med. Chem., 40, 2011-2016 (1997); Shan, et al., J. Pharm. Sci., 86(7), 765-767; Bagshawe, Drug Dev. Res, 34, 220-230 (1995); Bodor,Advances in Drug Res, 13, 224-331 (1984); Bundgaard, Design of Prodrugs(Elsevier Press 1985); Larsen, Design and Application of Prodrugs, DrugDesign and Development (Krogsgaard-Larsen et al, eds, Harwood AcademicPublishers, 1991): Dear et al., J. Chromatogr. B, 748, 281-293 (2000);Spraul et al., J. Pharmaceutical & Biomedical Analysis, 10, 601-605(1992); and Prox et al., Xenobiol., 3, 103-112 (1992).

Methods for co-administration with an additional therapeutic agent arewell known in the art (Hardman, et al. (eds.) (2001) Goodman andGilman's The Pharmacological Basis of Therapeutics, 10th ed.,McGraw-Hill, New York, N.Y.; Poole and Peterson (eds.) (2001)Pharmacotherapeutics for Advanced Practice: A Practical Approach,Lippincott, Williams & Wilkins, Phila., Pa.; Chabner and Longo (eds.)(2001) Cancer Chemotherapy and Biotherapy, Lippincott, Williams &Wilkins, Phila., Pa.). Generally, co-administration or administrationtogether indicates treating a subject with two or more agents, where theagents can be administered simultaneously or at different times. Forexample, such agents may be delivered to a single subject as separateadministrations, which may be at essentially the same time or differenttimes, and which may be by the same route or different routes ofadministration. Such agents may be delivered to a single subject in thesame administration (e.g., same formulation) such that they areadministered at the same time by the same route of administration.

Generally, each administration of a compound of the invention comprisesbetween about 10 mg to about 2000 mg in an individual, e.g., from about10 mg to about 50 mg, from about 50 mg to about 100 mg, from about 100mg to about 250 mg, from about 250 mg to about 500 mg, from about 500 mgto about 1000 mg, from about 1000 mg to about 2000 mg.

General Methods

All synthetic chemistry was performed in standard laboratory glasswareunless indicated otherwise in the examples. Commercial reagents wereused as received. Microwave reactions were performed in a BiotageInitiator using the instrument software to control heating time andpressure. Analytical LC/MS was performed on an Agilent 1290 infinity,Mass: 6150 SQD(ESI/APCI) or an Agilent 1200 SERIES, Mass:6130SQD(ESI/APCI); variable wavelength detector and Agilent 6130 singlequadrupole mass spectrometer, alternating positive and negative ionscans using Chemistation software. Retention times were determined fromthe extracted 220 nm UV chromatogram. HPLC was performed on a Waters2695 system with a variable wavelength detector using Empower software.Retention times were determined from the extracted 210 nm and 300 nm UVchromatograms. ¹H NMR was performed on a Bruker Avance 400 at 400 MHz ora Bruker Avance DRX-500 at 500 MHz using Topspin software. Forcomplicated splitting patterns, the apparent splitting was tabulated.Analytical thin layer chromatography was performed on silica(Macherey-Nagel ALUGRAM Xtra SIL G, 0.2 mm, UV₂₅₄ indicator) and wasvisualized under UV light. Silica gel chromatography was performedmanually, or with Grace automated chromatography for gradient elution.Melting points were collected using a Büchi B-540 melting pointapparatus.

EXAMPLES Example 1: Compounds 1, 2 and 32-amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 1

2-amino-9-((2R,3R,5S)-3-hydroxy-5-((R)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 2

2-amino-9-((2R,3R,5S)-3-hydroxy-5-((R)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(propa-1,2-dien-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 3

Compound 1, 2 and 3 were prepared according to the following multi-stepprocedures.

Preparation of (3R,5S)-5-(1-acetoxypropyl)tetrahydrofuran-2,3-diyldiacetate Intermediate (7S)

Step-1:O-((3aR,5R,6S,6aR)-5-((R)-2,2-Dimethyl-1,3-dioxolan-4-yl)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-6-yl)S-methyl carbonodithioate (1S)

To a suspension of NaH (60% in mineral oil, 36 g, 0.961 mol) in THF (500mL) at 0° C. was added a solution of commercially available(3aR,5S,6S,6aR)-5-((R)-2,2-dimethyl-1,3-dioxolan-4-yl)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-6-ol[582-52-5](100 g, 0.384 mol) and imidazole (1.3 g, 1.92 mmol) in THF(500 mL) dropwise. The reaction mixture was stirred at 10° C. for 15min. To this mixture was added carbon disulfide (121 mL, 1.92 mol) andthe reaction mixture was stirred at RT for 1 h, followed by iodomethane(118 mL, 1.92 mol) at 0° C. Stirring was continued at RT for 2 hwhereupon the reaction mixture was quenched with sat. NH₄Cl solution (1L) and extracted with EtOAc (2×1.5 L). The combined organic layers weredried over Na₂SO₄ and concentrated under reduced pressure. The residuewas purified by column chromatography over silica gel (100-200 mesh,eluting with 5% EtOAc in Pet-ether) to afford 120 g (89%) ofO-((3aR,5R,6S,6aR)-5-((R)-2,2-dimethyl-1,3-dioxolan-4-yl)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-6-yl)S-methyl carbonodithioate (1S) [1667-96-2] as a colorless oil. ¹H NMR(500 MHz, CDCl₃): δ 5.92-5.91 (m, 2H), 4.68-4.67 (m, 1H), 4.34-4.29 (m,2H), 4.12-4.04 (m, 2H), 2.59 (s, 3H), 1.61 (s, 3H), 1.54 (s, 3H),1.33-1.32 (m, 6H).

Step-2:(3aR,5S,6aR)-5-((R)-2,2-dimethyl-1,3-dioxolan-4-yl)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxole(2S)

A solution ofO-((3aR,5R,6S,6aR)-5-((R)-2,2-dimethyl-1,3-dioxolan-4-yl)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-6-yl)S-methyl carbonodithioate (1S) (120 g, 342 mmol) in toluene (800 mL) wasdegassed with argon for 45 min. A solution of AIBN (39 g, 239 mmol) andnBu₃SnH (150 mL, 411 mmol) in toluene (400 mL) was degassed with argonfor 30 min in a separate flask. This solution was added dropwise to thesolution of (1S) in toluene. The reaction mixture was stirred at 120° C.for 6 h and then cooled to RT. Toluene was removed under reducedpressure and the residue was partitioned between acetonitrile and hexane(1:1, 1000 mL). The acetonitrile layer was washed with hexane (3×500mL), and concentrated to give a residue that was purified by columnchromatography on silica gel (100-200 mesh, eluting with 10% EtOAc inPet-ether) to afford 70 g (83.7%) of(3aR,5S,6aR)-5-((R)-2,2-dimethyl-1,3-dioxolan-4-yl)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxole(2S) [4613-62-1] as a colorless oil. ¹H NMR (400 MHz, CDCl₃): δ 5.82 (d,J=3.6 Hz, 1H), 4.76-4.74 (m, 1H), 4.17-4.10 (m, 3H), 3.84-3.81 (m, 1H),2.21-2.16 (m, 1H), 1.80-1.73 (m, 1H), 1.54 (s, 3H), 1.51 (s, 3H), 1.36(s, 3H), 1.32 (s, 3H).

Step-3:(R)-1-((3aR,5S,6aR)-2,2-Dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethane-1,2-diol(3S)

A solution of(3aR,5S,6aR)-5-((R)-2,2-dimethyl-1,3-dioxolan-4-yl)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxole(2S) (70 g, 286 mmol) in 60% AcOH in water (350 mL, 5 Vol) was stirredat RT for 16 h. AcOH was removed under vacuum and the residue waspartitioned between Acetonitrile and hexane (1:1, 500 mL). Theacetonitrile layer was washed with hexane (3×300 mL), and theacetonitrile layer was concentrated. The residue was purified by columnchromatography on silica gel (100-200 mesh, eluting with 50% EtOAc inPet-ether) to afford 35 g (60%) of(R)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethane-1,2-diol(3S) [4005-46-3] as a colorless oil. ¹H NMR (500 MHz, DMSO-d₆): δ 5.81(d, J=3.5 Hz, 1H), 4.75 (t, J=4 Hz, 1H), 4.25-4.21 (m, 1H), 3.94-3.91(m, 1H), 3.74-3.71 (m, 1H), 3.62-3.58 (m, 1H), 2.08-2.00 (m, 1H),1.88-1.82 (m, 1H), 1.54 (s, 3H), 1.32 (s, 3H).

Step-4:(3aR,5S,6aR)-2,2-Dimethyltetrahydrofuro[2,3-d][1,3]dioxole-5-carbaldehyde(4S)

To a solution of(S)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethane-1,2-diol(3S) (3.3 g, 16.17 mmol) in methanol (35 mL) cooled by ice was addedsodium metaperiodate (4.15 g, 19.411 mmol). After the reaction mixturewas stirred at room temperature for 16 h, the resulting suspension wasfiltered. The filtrate was concentrated in vacuum and resultant residuewas purified by column chromatography on silica gel (eluting with 1:2EtOAc in Pet-ether) to afford 2.5 g of(3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxole-5-carbaldehyde(4S) [4613-68-7] as an colourless oil which was used immediately in thenext step.

Step-5:1-((3aR,5S,6aR)-2,2-Dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propan-1-ol(5S)

To a solution of(3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxole-5-carbaldehyde(4S) (2.6 g (crude), 15.11 mmol) in THE (30 mL) was added ethylmagnesium bromide (1M in THF, 15.1 mL, 15.11 mmol) at −20° C. underargon. After being stirred at room temperature for 16 h the reactionmixture was quenched with saturated NH₄Cl solution and extracted withEtOAc (3×100 mL). The combined organic layers were concentrated invacuum and the resultant crude compound was purified by columnchromatography on silica gel (eluting with 1:4 EtOAc in Pet-ether) toafford 2.1 g of1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propan-1-ol(5S) (mixture of diastereomers) as a colourless oil: ¹H NMR (400 MHz,CDCl₃): δ 5.80 (t, J=3.2 Hz, 1H), 4.75 (t, J=4.2 Hz, 1H), 4.23-4.13 (m,1H), 3.86-3.83 (m, 1H), 3.41-3.38 (m, 1H), 2.07-2.00 (m, 2H), 1.84-1.75(m, 1H), 1.59-1.47 (m, 4H), 1.32 (s, 3H), 1.01 (t, J=7.4 Hz, 3H).

Step-6:1-((3aR,5S,6aR)-2,2-Dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propylacetate (6S)

To a solution of1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propan-1-ol(5S) (2.1 g, 10.39 mmol) in CH₂Cl₂ (20 mL) was added Et₃N (2.9 mL, 20.79mmol), DMAP (253 mg, 2.07 mmol). The stirred solution was cooled to 0°C. for 10 min at which time Ac₂O (1.48 mL, 15.59 mmol) was added. Thereaction mixture was warmed to room temperature and stirred for 16 h.The reaction was quenched with aqueous sat. NaHCO₃ and extracted withCH₂Cl₂ (3×100 mL). The combined organic layers were dried over Na₂SO₄,and concentrated under vacuum to afford 2.4 g of1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propylacetate (6S) (mixture of diastereomers) as a colorless oil. The productwas used in the next step as is.

Step-7: (3R,5S)-5-(1-Acetoxypropyl)tetrahydrofuran-2,3-diyl diacetate(7S)

To1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propylacetate (6S) (2.4 g, 9.836 mmol) in dichloromethane (30 mL) was addedAcOH (5.62 mL, 98.36 mmol), Ac₂O (4.68 mL, 49.18 mmol) and conc. H₂SO₄(0.5 mL) at 0° C. The reaction mixture was warmed to room temperatureand stirred for 3 h. The reaction mixture was quenched with aqueous sat.NaHCO₃ and extracted with dichloromethane (3×100 mL). The combinedorganic layers were dried over Na₂SO₄ and concentrated in vacuum. Theresultant residue was purified by flash chromatography (SiO₂, 0 to 15%EtOAc-Pet-ether) to afford 1.5 g of(3R,5S)-5-(1-acetoxypropyl)tetrahydrofuran-2,3-diyl diacetate (7S)(mixture of diastereomers) as a colorless oil: ¹H NMR (400 MHz, CDCl₃):δ 6.12 (m, 1H), 5.19 (m, 1H), 4.91-4.83 (m, 1H), 4.44-4.34 (m, 1H),2.19-2.09 (m, 9H), 1.74-1.51 (m, 2H), 1.48 (s, 2H), 0.94 (t, J=7.4 Hz,3H).

Step-8: 6-Chloro-N⁴-(4-methoxybenzyl)pyrimidine-2,4,5-triamine (1)

4-Methoxybenzyl amine (114.8 g, 83.728 mol) was added to a stirredsolution mixture of 4,6-dichloropyrimidine-2,5-diamine [55583-59-0] (100g, 55.81 mol) and TEA (169 mL, 167.45 mol) in ethanol (1.0 L) at 0° C.and the resulting reaction mixture was stirred at reflux temperature for18 h. The solvent was evaporated under reduced pressure, the thick masswas poured into ice cold water and stirred for 30 min. The precipitatedsolid was collected by filtration, washed with water and dried undervacuum to afford 6-chloro-N⁴-(4-methoxybenzyl)pyrimidine-2,4,5-triamine(1) (100 g, 64%) as a brown solid. ES+, m/z 280.1 [M+H]⁺; C₁₂H₁₄ClN₅O;¹H NMR (500 MHz, DMSO-d₆): δ 8.25 (d, J=8.5 Hz, 2H), 6.92 (t, J=6.0 Hz,1H), 7.87 (d, J=8.5 Hz, 2H), 5.63 (s, 2H), 4.47 (d, J=5.5 Hz, 2H), 3.91(s, 2H), 3.72 (s, 3H).

Step-9: 2-Amino-6-chloro-9-(4-methoxybenzyl)-7,9-dihydro-8H-purin-8-one(2)

A mixture of 6-chloro-N⁴-(4-methoxybenzyl)pyrimidine-2,4,5-triamine (1)(50 g, 17.92 mol) and 1,1′-carbonyldiimidazole (100 g, 61.64 mol) inacetonitrile (500 mL) was stirred at reflux temperature for 18 h. Thereaction mixture was cooled to room temperature and concentrated underreduced pressure. To the resulting residue was added ice cold water andstirred for 30 min at room temperature. The precipitated solid wasfiltered, washed with water and dried to afford2-amino-6-chloro-9-(4-methoxybenzyl)-7,9-dihydro-8H-purin-8-one (2) (50g, 91%) as a brown solid; C₁₃H₁₂ClN₅O₂; ¹H NMR (500 MHz, DMSO-d₆): δ11.31 (s, 1H), 7.23 (d, J=9.0 Hz, 2H), 6.88 (d, J=5.0 Hz, 2H), 6.62 (s,2H), 4.80 (s, 2H), 3.71 (s, 3H).

Step-10:2-Amino-6-(benzyloxy)-9-(4-methoxybenzyl)-7,9-dihydro-8H-purin-8-one (3)

Sodium hydroxide (9.967 g, 262.29 mmol) was added to suspension of2-amino-6-chloro-9-(4-methoxybenzyl)-7,9-dihydro-8H-purin-8-one (2) (40g, 131.14 mmol) in benzyl alcohol (45.0 mL). The resulting reactionmixture was stirred at 120° C. for 18 h. The reaction mixture wasquenched with ice water (200 mL), added diethyl ether (150 mL) andstirred for 15 min. The resulting precipitated solid was filtered,washed with water and dried to afford2-amino-6-(benzyloxy)-9-(4-methoxybenzyl)-7,9-dihydro-8H-purin-8-one (3)(30 g, 60%) as an brown solid. ES+, m/z 378.1 [M+H]⁺; C₂₀H₁₉N₅O₃; ¹H NMR(400 MHz, DMSO-d₆): δ 10.81 (s, 1H), 7.48 (d, J=7.2 Hz, 2H), 7.40-7.36(t, J=7.6 Hz, 2H), 7.34-7.31 (t, J=5.2 Hz, 1H), 7.21 (d, J=8.4 Hz, 2H),6.87 (d, J=8.4 Hz, 2H), 6.27 (s, 2H), 5.41 (s, 2H), 4.78 (s, 2H), 3.71(s, 3H).

Step-11:2-Amino-6-(benzyloxy)-9-(4-methoxybenzyl)-7-(prop-2-yn-1-yl)-7,9-dihydro-8H-purin-8-one(4)

Propargyl bromide (7.1 ml, 63.66 mmol) was added to a suspension of2-amino-6-(benzyloxy)-9-(4-methoxybenzyl)-7,9-dihydro-8H-purin-8-one (3)(20 g, 53.05 mmol), K₂CO₃ (10.98 g, 79.57 mmol) in DMF (100 mL) at 0° C.and stirred at room temperature for 18 h. The reaction mixture wasquenched with ice water (200 mL), added diethyl ether (150 mL) andstirred for 15 min. The resulting precipitated solid was filtered,washed with water and dried to afford2-amino-6-(benzyloxy)-9-(4-methoxybenzyl)-7-(prop-2-yn-1-yl)-7,9-dihydro-8H-purin-8-one(4) (20 g, 91%) as a brown solid. ES+, m/z 416.1 [M+H]⁺; C₂₃H₂₁N₅O₃; ¹HNMR (400 MHz, DMSO-d₆): δ 7.52 (d, J=7.2 Hz, 2H), 7.38 (t, J=7.6 Hz,2H), 7.32 (t, J=5.2 Hz, 1H), 7.22 (d, J=8.4 Hz, 2H), 6.81 (d, J=8.4 Hz,2H), 6.27 (s, 2H), 5.44 (s, 2H), 4.82 (s, 2H), 4.56 (s, 2H), 3.71 (s,3H), 3.32-3.26 (m, 1H).

Step-12: 2-Amino-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione (5)

Trifluoromethanesulfonic acid (27 g, 180.72 mmol) was added to asuspension of2-amino-6-(benzyloxy)-9-(4-methoxybenzyl)-7-(prop-2-yn-1-yl)-7,9-dihydro-8H-purin-8-one(4) (25 g, 60.24 mmol) in trifluoroacetic acid (21 mL, 180.72 mmol) at0° C. under argon atmosphere and the resulting reaction mixture wasstirred at room temperature for 18 h under argon atmosphere. Thereaction mixture was quenched with ice cold water, basified with satNaHCO₃ solution under vigorous stirring and filtered. The residual solidwas taken into ethyl acetate, stirred for 30 min and filtered and driedto afford 2-amino-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione (5)(12 g, 36%) as a brown solid. ES+, m/z 206.1 [M+H]⁺; C₈H₇N₅O₂; ¹H NMR(400 MHz, DMSO-d₆): δ 11.32 (s, 1H), 6.74 (s, 2H), 4.53 (s, 2H), 3.14(s, 1H).

Step-13:N-(6,8-Dioxo-7-(prop-2-yn-1-yl)-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide(6)

Acetic anhydride (4.85 mL, 47.56 mmol) was added to a solution of2-amino-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione (5) (6.5 g,31.70 mmol) in DMF (65 mL) at room temperature under argon atmosphereand the resulting reaction mixture was stirred at room temperature for18 h under argon atmosphere. The reaction mixture was cooled to 0° C.(solid was formed under stirring) and stirred for 30 minutes. Theproduct was filtered, washed with ethanol and dried under vacuum toaffordN-(6,8-dioxo-7-(prop-2-yn-1-yl)-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide(6) (4 g, 51.2%) as an brown solid. ES+, m/z 248.1 [M+H]⁺; C₁₀H₉N₅O₃; ¹HNMR (400 MHz, DMSO-d₆): δ 11.83 (s, 2H), 4.61 (s, 2H), 3.23 (s, 1H),2.16 (s, 3H).

Step-14:(S)-1-((2S,4R,5R)-5-(2-Acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)propylacetate (7A) and(R)-1-((2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)propylacetate (7B)

ToN-(6,8-dioxo-7-(prop-2-yn-1-yl)-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide(6) (700 mg, 2.834 mmol) and(3R,5S)-5-(1-acetoxypropyl)tetrahydrofuran-2,3-diyl diacetate (7S) (979mg, 3.40 mmol) dissolved in 1,2-dichloroethane (10 mL) was addedbis(trimethylsilyl)acetamide (2.14 mL, 8.502 mmol). The reaction mixturewas stirred at 80° C. for 30 min under argon and then allowed to cool toroom temperature. The 1,2-dichloroethane was removed under vacuum andthe residue was taken up in MeCN (10 mL) whereupon trimethylsilyltrifluoromethanesulfonate (0.08 mL, 0.437 mmol) was added. The reactionmixture was heated to 80° C. and stirred for 16 h, cooled to roomtemperature, diluted with water and extracted with EtOAc (3×100 mL). Thecombined organic layers were washed with water (100 mL), brine (100 mL),dried over Na₂SO₄ and concentrated. The crude compound was purified byreverse phase prep-HPLC (Waters Prep-HPLC (Empower-3 software) (Column:X-SELECT-C18 (250*19), 5 u Mobile phase: 10 mM Ammonium bicarbonate inH₂O:MeCN GRADIENT: (T % B): 0/25, 8/45, 12/45, 12.1/98, 14/98, 14.1/25,17/25 Flow Rate: 15 ml/Min Diluent: MeCN+H₂O+THF+MeOH) to afford(S)-1-((2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)propylacetate (7A) (90 mg) ES+, m/z 476.2 [M+H]⁺; C₂₁H₂₅N₅O₈ and(R)-1-((2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)propylacetate (7B) (90 mg) ES+, m/z 476.2 [M+H]⁺; C₂₁H₂₅N₅O₈, both asoff-white solids.

Step-15:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 1

To a solution(S)-1-((2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)propylacetate (7A) (90 mg, 0.189 mmol) in methanol (10 mL) was added K₂CO₃(104 mg, 0.757 mmol) at 0° C. The reaction mixture was stirred at roomtemperature for 16 h and then concentrated under vacuum. The residueobtained was purified by GRACE FLASH chromatography (Reverse phase using0.01% of formic acid in acetonitrile as eluent) to afford2-amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 1 (25 mg, 21%), as a white solid. ES⁻, m/z 348.1 [M−H];C₁₅H₁₉N₅O₅, ¹H NMR (500 MHz, DMSO-d₆): δ 11.38 (brs, 1H), 6.66 (s, 2H),5.51 (d, J=3.2 Hz, 1H), 5.38 (d, J=4.4 Hz, 1H), 4.76-4.72 (m, 1H),4.68-4.66 (m, 1H), 4.59 (m, 2H), 4.02-3.98 (m, 1H), 3.27-3.25 (m, 1H),3.22-3.20 (m, 1H), 2.40-2.33 (m, 1H), 1.80-1.75 (m, 1H), 1.40-1.38 (m,1H), 1.31-1.25 (m, 1H), 0.95 (t, J=8.0 Hz, 3H).

Step-16:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((R)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-H-purine-6,8-dione,Compound 2 and2-amino-9-((2R,3R,5S)-3-hydroxy-5-((R)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(propa-1,2-dien-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 3

To a solution of(R)-1-((2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)propylacetate (7B) (90 mg, 0.189 mmol) in methanol (10 mL) was added K₂CO₃(104 mg, 0.757 mmol) at 0° C. The reaction mixture was stirred at roomtemperature for 16 h and then concentrated under vacuum. The residueobtained was purified by GRACE FLASH chromatography (Reverse phase using0.01% of formic acid in acetonitrile as eluent) to afford2-amino-9-((2R,3R,5S)-3-hydroxy-5-((R)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 2 (15 mg), as a white solid. ES⁻, m/z 348.1 [M−H]; C₁₅H₁₉N₅O₅,¹H NMR (500 MHz, DMSO-d₆): δ 10.99 (brs, 1H), 6.54 (s, 2H), 5.49 (d,J=3.6 Hz, 1H), 5.37 (d, J=4.8 Hz, 1H), 4.82-4.78 (m, 1H), 4.63-4.58 (m,3H), 3.96-3.91 (m, 1H), 3.41-3.36 (m, 1H), 3.23-3.22 (m, 1H), 2.45-2.39(m, 1H), 1.87-1.81 (m, 1H), 1.45-1.41 (m, 1H), 1.25-1.20 (m, 1H), 0.88(t, J=8.0 Hz, 3H). The isomerized propargyl biproduct,2-amino-9-((2R,3R,5S)-3-hydroxy-5-((R)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(propa-1,2-dien-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 3 (10 mg) was also isolated as an off-white solid. ES+, m/z350.1 [M+H]; C₁₅H₁₉N₅O₅, ¹H NMR (500 MHz, DMSO-d₆): δ 11.79 (brs, 1H),7.31 (t, J=6.5 Hz, 1H), 6.58 (s, 1H), 5.48 (d, J=4 Hz, 1H), 5.43 (d,J=6.5 Hz, 2H), 5.34 (d, J=5 Hz, 1H), 4.79 (s, 1H), 4.78-4.77 (m, 1H),3.96-3.93 (m, 1H), 3.41-3.39 (m, 1H), 2.40-2.36 (m, 1H), 1.85-1.81 (m,1H), 1.42-1.40 (m, 1H), 1.25-1.21 (m, 2H), 0.87 (t, J=7.5 Hz, 3H).

Alternative Synthetic Procedures for Compound 1.

Example 2:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 1

Compound 1 was also synthesized according to the following alternativemulti-step procedure.

Step-1:(R)-2-((3aR,5S,6aR)-2,2-Dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)-2-hydroxyethyl4-methylbenzenesulfonate (8S)

To a solution of(R)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethane-1,2-diol(3S) (25 g, 122 mmol) in dry pyridine (250 mL) was addedp-toluenesulfonyl chloride (34.7 g, 183 mmol) at 0° C. After beingstirred at room temperature for 12 h, pyridine was removed under vacuum.The residue was diluted with water (500 mL), extracted with EtOAc (2×600mL). The combined EtOAc layer was dried over Na₂SO₄ and concentrated.The concentrate was purified by column chromatography on silica gel(100-200 mesh, eluting with 25% EtOAc in petroleum ether) to afford 26.4g (60%) of(R)-2-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)-2-hydroxyethyl4-methylbenzenesulfonate (8S) [5875-16-4] as a light yellow oil. ¹H NMR(500 MHz, CDCl₃): δ 7.80 (d, J=6.5 Hz, 2H), 7.36 (d, J=8.00 Hz, 2H),5.76 (d, J=4 Hz, 1H), 4.72 (t, J=4.00 Hz, 1H), 4.17-4.14 (m, 2H),4.01-3.97 (m, 2H), 2.45 (s, 3H), 2.41 (d, J=4 Hz, 1H), 2.10-2.04 (m,1H), 1.80-1.75 (m, 1H), 1.51 (s, 3H), 1.33 (s, 3H).

Step-2:(3aR,5S,6aR)-2,2-Dimethyl-5-((R)-oxiran-2-yl)tetrahydrofuro[2,3-d][1,3]dioxole(9S)

To a solution of(R)-2-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)-2-hydroxyethyl4-methylbenzenesulfonate (3S) (26 g, 72 mmol) in anhydrous THE (260 mL)cooled at −78° C. was added potassium bis(trimethylsilyl)amide (108 mL,108 mmol, 1 M in THF) under N₂ atmosphere. After being stirred at −78°C. for 1 h, the reaction mixture was poured into saturated NH₄Clsolution. The organic layer was separated and the aqueous phase wasextracted with EtOAc (2×200 mL). The combined organic layers were driedover Na₂SO₄ and concentrated in vacuum. The crude product was purifiedby column chromatography on silica gel (100-200 mesh, eluting with 25%EtOAc in petroleum ether) to afford 10.5 g (78%) of(3aR,5S,6aR)-2,2-dimethyl-5-((R)-oxiran-2-yl)tetrahydrofuro[2,3-d][1,3]dioxole(9S) [2457-93-4] as a light yellow oil. ¹H NMR: (400 MHz, CDCl₃): δ 5.84(d, J=5.4 Hz, 1H), 4.75 (t, J=4.4 Hz, 1H), 4.23-4.18 (m, 1H), 3.15-3.13(m, 1H), 2.83-2.80 (m, 1H), 2.61 (m, 1H), 2.07 (dd, J=13.2, 4.8 Hz, 1H),1.75-1.68 (m, 1H), 1.50 (s, 3H), 1.32 (s, 3H).

Step-3:(R)-1-((3aR,5S,6aR)-2,2-Dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propan-1-ol(10S)

To a suspension of CuI (2 g, 10.7 mmol) in dry TH (300 mL) under N₂atmosphere was added methylmagnesium bromide (3 M in diethyl ether, 53mL, 159 mmol) at −78° C. After being stirred at −78° C. for 1 hour, asolution of(3aR,5S,6aR)-2,2-dimethyl-5-((R)-oxiran-2-yl)tetrahydrofuro[2,3-d][1,3]dioxole(9S) (10 g, 53 mmol) in THE (40 mL) was added and stirred at −78° C. foran additional 2 hours. The reaction mixture was poured into saturatedNH₄Cl solution (200 mL) and the organic layer was separated. The aqueousphase was extracted with EtOAc (2×200 mL) and the organic layers werecombined, dried over Na₂SO₄ and concentrated in vacuum. The crudeproduct was purified by column chromatography on silica gel (100-200mesh, eluting with 30% EtOAc in petroleum ether) to afford 8.2 g (75%)of(R)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propan-1-ol(10S) as a light yellow oil. ¹H NMR (500 MHz, CDCl₃): δ 5.81 (d, J=3.5Hz, 1H), 4.75-4.73 (m, 1H), 4.23-4.19 (m, 1H), 3.85-3.84 (m, 1H),2.04-2.02 (m, 1H), 1.91-1.90 (m, 2H), 1.51 (s, 3H), 1.45-1.39 (m, 2H),1.32 (s, 3H), 1.01 (t, J=7.5 Hz, 3H).

Step-4:(S)-1-((3aR,5S,6aR)-2,2-Dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propyl4-nitrobenzoate (11S)

To a stirred solution of(R)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propan-1-ol(10S) (8 g, 39 mmol), triphenylphosphine (31 g, 118 mmol),4-nitrobenzoic acid (20 g, 118 mmol) in TH (240 mL) was addeddiethylazodicarboxylate (18.6 mL, 118 mmol) drop wise at 0° C. under N₂atm. After being stirred at RT for 10 h, the mixture was quenched byaddition of saturated NaHCO₃ solution (200 mL) and extracted with EtOAc(2×200 mL). The organic layers were combined, dried over Na₂SO₄ andconcentrated in vacuum. The residue was purified by columnchromatography on silica gel (100-200 mesh, eluting with 15% EtOAc inpetroleum ether) to afford 9 g (64.7%) of(S)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propyl4-nitrobenzoate (11S) as a light yellow solid. ¹H NMR (400 MHz, CDCl₃):δ 8.34-8.27 (m, 2H), 8.25-8.21 (m, 2H), 5.83 (d, J=3.6 Hz, 1H),5.20-5.15 (m, 1H), 4.73 (t, J=4.0 Hz, 1H), 4.40-4.38 (m, 1H), 2.12 (dd,J=13.2, 3.6 Hz, 1H), 1.88-1.78 (m, 2H), 1.68-1.62 (m, 1H), 1.55 (s, 3H),1.32 (s, 3H), 1.01 (t, J=7.2 Hz, 3H).

Step-5:(S)-1-((3aR,5S,6aR)-2,2-Dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propan-1-ol(12S)

To a stirred solution of(S)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propyl4-nitrobenzoate (11S) (9 g, 26 mmol) in methanol (180 mL) was addedK₂CO₃ (7.5 g, 55 mmol). After being stirred at room temperature for 30minutes, the resultant mixture was filtered and the filtrate wasconcentrated under vacuum. The crude material was purified by columnchromatography on silica gel (100-200 mesh, eluting with 30% EtOAc inpetroleum ether) to afford 4.5 g (87%) of(S)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propan-1-ol(12S) as a light yellow oil. ¹H NMR (400 MHz, CDCl₃): δ 5.81 (d, J=3.6Hz, 1H), 4.74 (t, J=4.4 Hz, 1H), 4.17-4.13 (m, 1H), 3.42-3.38 (m, 1H),2.05-2.00 (m, 2H), 1.80-1.71 (m, 1H), 1.57-1.50 (m, 5H), 1.32 (s, 3H),1.01 (t, J=7.6 Hz, 3H).

Step-6:(S)-1-((3aR,5S,6aR)-2,2-Dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propylacetate (13S)

To a stirred solution of(S)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propan-1-ol(12S) (4.5 g, 22 mmol), TEA (31 mL, 267 mmol) and DMAP (0.538 g, 4.4mmol) in anhydrous DCM (90 mL) was added acetic anhydride (20 g, 198mmol). After being stirred at room temperature for 10 h the reaction wasquenched with a saturated aq. NaHCO₃ solution (100 mL). The organiclayer was separated and the aqueous phase was extracted with DCM (2×100mL). The combined organic layers were dried over Na₂SO₄ and concentratedunder vacuum. The crude product was purified by column chromatography onsilica gel (100-200 mesh, eluting with 20% EtOAc in petroleum ether) toafford 4.4 g (80.5%) of(S)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propylacetate (13S) as a colorless oil. ¹H NMR (400 MHz, CDCl3): δ 5.80 (d,J=3.6 Hz, 1H), 4.9-4.87 (m, 1H), 4.72 (t, J=4.4 Hz, 1H), 4.30-4.25 (m,1H), 2.10 (s, 3H), 2.03-1.99 (m, 1H), 1.69-1.55 (m, 3H), 1.51 (s, 3H),1.32 (s, 3H), 0.91 (t, J=4.0 Hz, 3H). Step-7:(3R,5S)-5-((S)-1-Acetoxypropyl)tetrahydrofuran-2,3-diyl diacetate (14S)

To a solution of(S)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propylacetate (13S) (4.4 g, 18 mmol), acetic acid (10.4 mL, 180 mmol) andacetic anhydride (8.8 mL, 90 mmol) in anhydrous DCM (90 mL) was addedconcentrated H₂SO₄ (0.44 mL) at 0° C. After being stirred at RT for 3hours, the reaction was quenched by addition of saturated aq·NaHCO₃solution (100 mL). The organic layer was separated and the aqueous phasewas extracted with DCM (2×100 mL). The combined organic layers weredried over Na₂SO₄ and concentrated under vacuum. The crude product waspurified by column chromatography on silica gel (100-200 mesh, elutingwith 30% EtOAc in petroleum ether) to afford 2.7 g (52%) of(3R,5S)-5-((S)-1-acetoxypropyl)tetrahydrofuran-2,3-diyl diacetate (14S)as a colorless oil. ¹H NMR (400 MHz, CDCl₃): δ 6.10 (s, 1H), 5.18 (d,J=4.4 Hz, 1H), 4.87-4.82 (m, 1H), 4.44-4.34 (m, 1H), 2.12-2.10 (m, 9H),1.61-1.54 (m, 4H), 0.94 (m, 3H).

Step-8:(S)-1-((2S,4R,5R)-5-(2-Acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)propylacetate (7A)

ToN-(6,8-dioxo-7-(prop-2-yn-1-yl)-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide(6) (300 mg, 1.21 mmol),(3R,5S)-5-((S)-1-acetoxypropyl)tetrahydrofuran-2,3-diyl diacetate (14S)(384 mg, 1.33 mmol) dissolved in 1,2-dichloroethane (20 mL) was addedbis(trimethylsilyl)acetamide (0.91 mL, 3.63 mmol). The resultingreaction mixture was stirred at 80° C. for 30 min under argon. Thereaction mixture was allowed to warm to RT and 1,2-dichloroethane wasremoved under vacuum. The residue was taken up in ACN (20 mL) andtrimethylsilyl trifluoromethanesulfonate (0.335 mL, 1.815 mmol) wasadded. The reaction mixture was heated at 80° C. for 16 h. The reactionmixture was cooled to room temperature and concentrated under vacuum.The residue was diluted with aq·NaHCO₃ (50 mL) and extracted with EtOAc(3×50 mL). The combined EtOAc layers were washed with water (30 mL),brine (30 mL), dried over Na₂SO₄ and concentrated under vacuum. Thecrude compound was purified by GRACE flash chromatography (using 80%EtOAc in pet ether as eluant) to afford 200 mg (34.6%) of(S)-1-((2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)propylacetate (7A) as an off-white solid. ES+, m/z 476.2 [M+H]⁺; C₂₁H₂₅N₅O₈.

Step-9:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 1

To a solution of(S)-1-((2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)propylacetate (7A) (200 mg, 0.421 mmol) in MeOH (20 mL) was added K₂CO₃ (232mg, 1.684 mmol) at 0° C. The reaction mixture was stirred at RT for 16h. Methanol was removed under reduced pressure at 30° C. The residue waspurified by normal phase GRACE flash chromatography (using 7% MeOH inDCM as eluant) followed by a reverse phase GRACE flash chromatography(using 0.01% aq. HCO₂H and ACN as eluent). The pure fractions uponlyophilization afforded 32 mg (22%) of2-amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 1 as an off white solid. ES⁺, m/z 350.2 [M+H]; C₁₅H₁₉N₅O₅: ¹HNMR (400 MHz, DMSO-d₆): δ 11.00 (brs, 1H), 6.55 (brs, 2H), 5.51 (d,J=4.0 Hz, 1H), 5.39 (d, J=5.2 Hz, 1H), 4.76-4.72 (m, 1H), 4.58-4.55 (m,3H), 4.02-3.98 (m, 1H), 3.31-3.30 (m, 1H), 3.23-3.22 (m, 1H), 2.39-2.33(m, 1H), 1.78-1.75 (m, 1H), 1.45-1.38 (m, 1H), 1.31-1.25 (m, 1H), 0.87(t, J=7.2 Hz, 3H).

Example 3:2-Amino-7-(cyclopropylmethyl)-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 4

Preparation of Intermediates (12) and (14)

Intermediate compounds (12) and (14) were synthesized according to thefollowing multi-step procedure.

Step-1:2-Amino-6-chloro-7-(cyclopropylmethyl)-9-(4-methoxybenzyl)-7,9-dihydro-8H-purin-8-one(8)

Cyclopropyl methyl bromide (32.9 g, 24.39 mol) was added to a suspensionof 2-amino-6-chloro-9-(4-methoxybenzyl)-7,9-dihydro-8H-purin-8-one (3)(62 g, 20.32 mol), K₂CO₃ (42 g, 30.49 mol) in DMF (500 mL) at 0° C. andthen stirred at room temperature for 18 h. The reaction mixture waspoured on to ice cold water and stirred for 30 mins at room temperature.The precipitated solid product was collected by filtration and driedunder vacuum to affored2-amino-6-chloro-7-(cyclopropylmethyl)-9-(4-methoxybenzyl)-7,9-dihydro-8H-purin-8-one(8) (60 g, 82%) as a brown solid. TLC: 30% Ethyl acetate in hexane;R_(f): 0.4; ES+, m/z 360.1 [M+H]⁺; C₁₇H₁₈ClN₅O₂; ¹H NMR (400 MHz,DMSO-d₆): δ 7.23 (d, J=8.4 Hz, 2H), 6.89 (d, J=8.8 Hz, 2H), 6.75 (s,2H), 4.86 (s, 2H), 3.80 (d, J=6.8 Hz, 2H), 3.71 (s, 3H), 1.21-1.17 (m,1H), 0.50-0.46 (m, 2H), 0.37-0.34 (m, 2H).

Step-2:2-Amino-6-chloro-7-(cyclopropylmethyl)-7,9-dihydro-8H-purin-8-one (9)

Anhydrous AlCl₃ powder (25 g, 187 mmol) was added to a stirred solutionof2-amino-6-chloro-7-(cyclopropylmethyl)-9-(4-methoxybenzyl)-7,9-dihydro-8H-purin-8-one(8) (50 g, 139.2 mmol) in 1,2-dichloro benzene (250 mL) at roomtemperature under argon atmosphere and the resulting reaction mixturewas stirred at 100° C. for 18 h under argon atmosphere. The reactionmixture was cooled to room temperature and quenched with ice cold water,basified with a sat. NaHCO₃ solution under vigorous stirring andfiltered. The filtered solid was taken into 10% MeOH in dichloromethane,stirred for 30 min and filtered (repeated thrice with volume of 1.0 Lsolvent). The filterate was passed through a pad of celite andconcentrated under reduced pressure. The solid thus obtained was washedtwice with 10% methanol in dichloromethane and filtered. The filteredsolid was again washed with twice acetonitrile, filtered and dried toafford 2-amino-6-chloro-7-(cyclopropylmethyl)-7,9-dihydro-8H-purin-8-one(9) (12 g, 36%) as a brown solid. TLC: 50% Ethyl acetate in hexane;R_(f): 0.3; ES+, m/z 240.1 [M+H]⁺; C₉H₁₀ClN₅O. ¹H NMR (500 MHz,DMSO-d₆): δ 11.81 (s, 1H), 6.58 (s, 2H), 3.73-3.72 (d, J=7.0 Hz, 2H),1.21-1.17 (m, 1H), 0.50-0.46 (m, 2H), 0.37-0.34 (m, 2H). m.p. 286-290°C.

Step-3:2-Amino-6-(benzyloxy)-7-(cyclopropylmethyl)-7,9-dihydro-8H-purin-8-one(10)

Sodium metal (1.43 g, 62.6 mmol) was added to benzyl alcohol (25.0 mL)for 1 h (until all the sodium dissolved). The resulting viscous liquidwas cooled to rt and2-amino-6-chloro-7-(cyclopropylmethyl)-7,9-dihydro-8H-purin-8-one (9)(5.0 g, 20.86 mmol) was added. The resulting reaction mixture wasstirred at 100° C. for 1 h and quenched with ice water (200 mL). Diethylether (150 mL) was added and stirred for 15 min. The resultingprecipitated solid was filtered, washed with water and dried. The solidwas dissolved in 15% methanol-dichloromethane (500 mL), filtered throughcelite pad, washed with brine and concentrated. The resulting solid waswashed with diethyl ether and filtered to afford2-amino-6-(benzyloxy)-7-(cyclopropylmethyl)-7,9-dihydro-8H-purin-8-one(10) (3.5 g, 54%) as an off white solid. TLC: 70% Ethyl acetate in petether; R_(f): 0.6; ES+, m/z 312.2 [M+H]⁺; C₁₆H₁₇N₅O₂. ¹H NMR (500 MHz,DMSO-d₆): δ 11.30 (brs, 1H), 7.48-7.46 (m, 2H), 7.41-7.38 (m, 2H),7.35-7.30 (m, 1H), 6.15 (s, 2H), 5.41 (s, 2H), 3.56 (d, J=7.0 Hz, 2H),1.14-1.10 (m, 1H), 0.36-0.32 (m, 2H), 0.23-

Step-4: 2-Amino-7-(cyclopropylmethyl)-7,9-dihydro-1H-purine-6,8-dione(11)

A suspension of2-amino-6-(benzyloxy)-7-(cyclopropylmethyl)-7,9-dihydro-8H-purin-8-one(10) (10.0 g, 32.15 mmol), anhydrous LiBr (3.34 g, 38.58 mmol),chlorotrimethylsilane (4.53 g, 108.6 mmol) in acetonitrile (700 mL) werestirred at room temperature for 16 h. Methanol (60 mL) was added to thereaction mixture and stirred for 30 min. The solvent was distilled offto a reduced volume of ˜100 mL and filtered. The filter cake was washedwith acetonitrile and dried. The solid was taken into a sat. NaHCO₃solution (200 mL), stirred for 1 h, filtered, washed with water anddried. The solid was stirred in 10% methanol/dichloromethane (50 mL),filtered and dried to afford2-amino-7-(cyclopropylmethyl)-7,9-dihydro-1H-purine-6,8-dione (11) (8.5g, 80%) as a pale brown solid. TLC: 10% methanol in dichloromethane;R_(f): 0.4; ES+, m/z 222.1 [M+H]⁺; C₉H₁₁N₅O₂. ¹H NMR (500 MHz, DMSO-d₆):δ 11.06 (s, 1H), 10.68 (s, 1H), 6.36 (s, 2H), 3.58 (d, J=7.0 Hz, 2H),1.19-1.14 (m, 1H), 0.40-0.36 (m, 2H), 0.33-0.30 (m, 2H). m.p. 364-368°C.

Step-5:N-(7-(Cyclopropylmethyl)-6,8-dioxo-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide(12)

Acetic anhydride (0.13 mL, 1.3574 mmol) was added to a solution of2-amino-7-(cyclopropylmethyl)-7,9-dihydro-1H-purine-6,8-dione (11) (200mg, 0.9049 mmol) in acetic acid (5 mL) at ambient temperature underargon atmosphere and the resulting reaction mixture was heated at 140°C. for 6 h. The reaction mixture was cooled down to 0° C. (solid wasformed under stirring) and stirred for 30 minutes. The product wasfiltered, and dried under vacuum to affordN-(7-(cyclopropylmethyl)-6,8-dioxo-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide(12) (180 mg, 75.6%) as an brown solid: C₁₁H₁₃N₅O₃: LC-MS indicated 98%of desired m/z (M+H; 264.1). ¹H NMR (400 MHz, DMSO-d₆): δ 12.01 (s, 1H),11.68 (s, 1H), 11.65 (s, 1H), 3.66 (d, J=7.2 Hz, 2H), 2.15 (s, 3H),2.21-2.15 (m, 1H), 043-0.38 (m, 2H), 0.36-0.32 (m, 2H).

Step-6: 2-Amino-7-(cyclopropylmethyl)-7,9-dihydro-8H-purin-8-one (13)

10% Pd—C (5.0 g) was added to a solution of2-amino-6-chloro-7-(cyclopropylmethyl)-9-(4-methoxybenzyl)-7,9-dihydro-8H-purin-8-one(8) (20 g, mmol) in methanol (500 mL). The reaction mixture washydrogenated with H₂ gas at 80 psi of pressure in a Parr shaker vial atroom temperature for 24 h. The reaction mixture was filtered through acelite pad and the filtrate was evaporated to give crude product. To thecrude compound was added acetonitrile with stirred for 15 min, filtered.This step was repeated and the solid was dried under vacuum to afford2-amino-7-(cyclopropylmethyl)-7,9-dihydro-8H-purin-8-one (13) (11 g,64%) as an off white solid. TLC: 70% Ethyl acetate in hexane; R_(f):0.2; ES+, m/z 206.2 [M+H]⁺; C₉H₁₁N₅O. ¹H NMR (500 MHz, DMSO-d₆): δ 12.68(s, 1H), 8.11 (s, 1H), 7.87 (s, 2H), 3.60-3.59 (d, J=7.5 Hz, 2H),1.18-1.12 (m, 1H), 0.50-0.46 (m, 2H), 0.37-0.34 (m, 2H). m.p. 245-249°C.

Step-7:N-(7-(cyclopropylmethyl)-8-oxo-8,9-dihydro-7H-purin-2-yl)acetamide (14)

To a stirred solution of2-amino-7-(cyclopropylmethyl)-7,9-dihydro-8H-purin-8-one (13) (2 g, 9.75mmol) in AcOH (50 mL) was added Ac₂O (3.68 mL, 39.02 mmol). Theresulting solution was heated at 120° C. for 12 h. The reaction mixturewas cooled to RT and resulting solid was collected by filtration, washedwith diethyl ether (100 mL) and dried to obtain 1.6 g (51%) ofN-(7-(cyclopropylmethyl)-8-oxo-8,9-dihydro-7H-purin-2-yl)acetamide (14)as an orange solid. ES+, m/z 248.2 [M+H]⁺; C₁₁H₁₃N₅O₂: ¹H NMR (400 MHz,DMSO-d₆): δ 12.97 (s, 1H), 11.71 (s, 1H), 8.31 (s, 1H), 3.74, (d, J=7.2Hz, 2H), 2.22 (s, 3H), 1.45-1.13 (m, 1H), 0.53 (t, J=3.6 Hz, 2H), 0.48(t, J=3.6 Hz, 2H).

Step-8:(S)-1-((2S,4R,5R)-5-(2-Acetamido-7-(cyclopropylmethyl)-6,8-dioxo-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)propylacetate (15)

N-(7-(cyclopropylmethyl)-6,8-dioxo-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide(12) (200 mg, 0.7604 mmol),(3R,5S)-5-((S)-1-acetoxypropyl)tetrahydrofuran-2,3-diyl diacetate (14S)(219 mg, 0.7604 mmol) and bis(trimethylsilyl)acetamide (0.58 mL, 2.2812mmol) were dissolved in 1,2-dichloroethane (10 mL). The reaction mixturewas stirred at 80° C. for 30 min under argon followed by concentrationunder reduced pressure. The resultant residue was diluted with ACN (50mL), charged with TMSOTf (0.212 mL, 1.1406 mmol), placed into apreheated oil bath at 80° C., and stirred for 16 h. The reaction wascooled to room temperature and the solvent was removed by rotaryevaporation. The resultant solid was dissolved in ethyl acetate (100 mL)and extracted with saturated aqueous NaHCO₃ (2×30 mL). The organic phasewas dried with Na₂SO₄ and concentrated. The crude product was purifiedby flash chromatography (SiO₂, 0 to 80% EtOAc-pet-ether) to afford(S)-1-((2S,4R,5R)-5-(2-acetamido-7-(cyclopropylmethyl)-6,8-dioxo-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)propylacetate (15) (175 mg, 46.9%) as an light yellow solid: C₂₂H₂₉N₅O₈: ES+,m/z 492.2 [M+H]⁺. This compound was used further without any furtherpurification.

Step-9:2-Amino-7-(cyclopropylmethyl)-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 4

To a solution of(S)-1-((2S,4R,5R)-5-(2-acetamido-7-(cyclopropylmethyl)-6,8-dioxo-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)propylacetate (15) (175 mg, 0.3564 mmol) in methanol (10 mL) was added K₂CO₃(20 mg, 0.1424 mmol) at 0° C. The reaction mixture was stirred at roomtemperature for 36 h, concentrated and purified by prep-HPLC (Column:X-SELECT-C18 (250*19), 5 u Mobile phase: 0.1% TFA in H₂O:ACN gradient:(T % B):—0/5, 1/5, 8/40, 9/40, 9.1/98, 11/98, 11.1/5, 14/5 Flow Rate: 20m). Pure fractions were collected and lyophilized to afford2-amino-7-(cyclopropylmethyl)-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 4 (60 mg, 47.6%), as a white solid. C₁₆H₂₃N₅O₅: ES⁺, m/z 366.2[M+H]⁺. ¹H NMR (500 MHz, DMSO-d₆): δ 10.87 (s, 1H), 6.45 (s, 2H), 5.52(s, 1H), 4.76-4.75 (m, 1H), 4.01-3.97 (m, 1H), 3.64 (d, J=7 Hz, 2H),3.27-3.25 (m, 1H), 2.39-2.35 (m, 1H), 1.79-1.74 (m, 1H), 1.41-1.37 (m,1H), 1.28-1.17 (m, 2H), 0.88-0.85 (t, J=7 Hz, 3H), 0.40 (d, J=7.5 Hz,2H), 0.34 (d, J=3.5 Hz, 2H).

Example 4:2-Amino-7-(cyclopropylmethyl)-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7,9-dihydro-8H-purin-8-one,Compound 5

Compound 5 was prepared according to the following 2 step procedure.

Step-1:(S)-1-((2S,4R,5R)-5-(2-Acetamido-7-(cyclopropylmethyl)-8-oxo-7,8-dihydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)propylacetate (16)

A stirred solution ofN-(7-(Cyclopropylmethyl)-8-oxo-8,9-dihydro-7H-purin-2-yl)acetamide (14)(300 mg, 1.21 mmol),(3R,5S)-5-((S)-1-acetoxypropyl)tetrahydrofuran-2,3-diyl diacetate (14S)(384.7 mg, 1.33 mmol), bis(trimethylsilyl)acetamide (0.73 mL, 3.64 mmol)in 1,2-dichloroethane (25 mL) was heated to 80° C. for 30 min underargon. The reaction mixture was cooled to RT and 1,2-dichloroethane wasremoved under vacuum. The residue was dissolved in ACN (30 mL), TMSOTf(0.40 mL, 1.82 mmol) was added and the reaction mixture was maintainedat 80° C. for 16 h. The mixture was then cooled to room temperature andconcentrated under vacuum. The residue was diluted with aqueoussat·NaHCO₃ (50 mL) and extracted with EtOAc (3×50 mL). The combinedEtOAc layers were washed with water (30 mL), brine (30 mL), dried overNa₂SO₄ and concentrated under vacuum. The crude compound was purified bycolumn chromatography over silica gel (100-200 mesh) using 3% MeOH/DCMas eluant to afford 250 mg (53.6%) of(S)-1-((2S,4R,5R)-5-(2-acetamido-7-(cyclopropylmethyl)-8-oxo-7,8-dihydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)propylacetate (16) as a pale yellow solid. C₂₂H₂₉N₅O₇: ES⁺, m/z 476.1 [M+H]⁺.

Step 2:2-Amino-7-(cyclopropylmethyl)-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7,9-dihydro-8H-purin-8-one,Compound 5

To a stirred solution of(S)-1-((2S,4R,5R)-5-(2-acetamido-7-(cyclopropylmethyl)-8-oxo-7,8-dihydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)propylacetate (16) (250 mg, 0.526 mmol) in MeOH (15 mL) was added K₂CO₃ (145mg, 1.052 mmol) at 0° C. The reaction mixture was stirred at RT for 16 hand acetic acid (0.05 mL, 0.815 mmol) was added. The solution wasstirred for an additional 20 min and concentrated under reduced pressureat 30° C. The residue was purified by Prep HPLC (X-SELECT-C18 (250*19),5 u Mobile phase: 10 mM ammonium bicarbonate in H₂O:MeCN Gradient: (T %B):—0/20, 8/35, 11/35, 11/98, 13/98, 13.1/20, 16/20 Flow Rate: 18 ml) toafford 35 mg (46%) of2-amino-7-(cyclopropylmethyl)-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7,9-dihydro-8H-purin-8-one,Compound 5 as an off white solid. C₁₆H₂₃N₅O₄: ES⁺, m/z 350.1 [M+H]⁺. ¹HNMR (500 MHz, DMSO-d₆): δ 8.06 (s, 1H), 6.24 (brs, 2H), 5.64-5.60 (m,1H), 5.44 (bs, 1H), 4.82-4.79 (m, 1H), 4.61 (bs, 1H), 4.03-4.02 (m, 1H),4.03-4.01 (m, 1H), 3.62 (d, J=7.0 Hz, 2H), 3.31 (s, 1H), 2.49 (m, 1H),1.80-1.78 (m, 1H), 1.41-1.31 (m, 1H), 1.28-1.27 (m, 1H), 0.87 (t, J=7.0Hz, 3H), 0.51-0.46 (m, 2H), 0.36-0.33 (m, 2H).

Example 5:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-8H-purin-8-one,Compound 6

Preparation of Intermediate (21)

Intermediate compound (21) was synthesized according to the followingmulti-step procedure.

Step-1: N4-(4-Methoxybenzyl)pyrimidine-2,4,5-triamine (17)

10% Pd—C (10 g) was added to a solution of6-chloro-N₄-(4-methoxy-benzyl)-pyrimidine-2,4,5-triamine (1) (2.5 g,0.072 mol) in methanol (50 mL) and THF (150 mL). The reaction mixturewas hydrogenated with H₂ gas at 80 psi of pressure in a Parr shaker vialat room temperature for 24 h. The reaction mixture was filtered throughcelite pad and the filtrate was evaporated. The crude compound wasstirred in ethyl acetate (100 mL) for 15 min, the solid compound wascollected by filtration and dried under vacuum to affordN4-(4-methoxybenzyl)pyrimidine-2,4,5-triamine (17) (21.0 g, 95.8%), ES+,m/z 246.2 [M+H]⁺; C₁₂H₁₅N₅O; ¹H NMR (400 MHz, DMSO-d₆): δ 11.71 (bs,1H), 8.75-8.68 (m, 1H), 7.31 (d, J=8.4 Hz, 2H), 7.25 (bs, 2H), 7.07 (s,1H), 6.90 (d, J=8 Hz, 2H), 4.77 (bs, 2H), 4.56 (d, J=5.6 Hz, 2H), 3.73(s, 3H).

Step-2: 2-Amino-9-(4-methoxybenzyl)-7,9-dihydro-8H-purin-8-one (18)

A mixture of N4-(4-methoxybenzyl)pyrimidine-2,4,5-triamine (17) (23.0 g,9.39 mol) and 1,1′-carbonyldiimidazole (18.3 g, 11.27 mol) in THF (250mL) was stirred at room temperature for 18 h. The reaction mixture wasconcentrated under reduced pressure. To the resulting residue was addedice cold water and stirred for 30 min at room temperature. Theprecipitated solid was filtered, washed with water and dried undervacuum to afford (22.0 g, 86.6%) of2-amino-9-(4-methoxybenzyl)-7,9-dihydro-8H-purin-8-one (18) as a lightbrown solid. ES+, m/z 272.2 [M+H]⁺; C₁₃H₁₃N₅O₂; ¹H NMR (400 MHz,DMSO-d₆): δ 10.81 (s, 1H), 7.73 (s, 1H), 7.23 (d, J=8.0 Hz, 2H), 6.88(d, J=8.4 Hz, 2H), 6.19 (s, 2H), 4.80 (s, 2H), 3.72 (s, 3H).

Step-3:2-Amino-9-(4-methoxybenzyl)-7-(prop-2-yn-1-yl)-7,9-dihydro-8H-purin-8-one(19)

Propargyl bromide (87 mL, 77.49 mol) was added to a suspension of2-amino-9-(4-methoxybenzyl)-7,9-dihydro-8H-purin-8-one (18) (17.5 g,6.46 mol) and K₂CO₃ (13.4 g, 9.69 mol) in DMF (175 mL) at 0° C. andstirred at room temperature for 18 h. The reaction mixture was quenchedwith ice water (400 mL) and stirred for 30 min. The resultingprecipitated solid was filtered, washed with water and dried undervacuum to afford2-amino-9-(4-methoxybenzyl)-7-(prop-2-yn-1-yl)-7,9-dihydro-8H-purin-8-one(19) (17.5 g, 86.68%) as a brown solid. ES⁺, m/z 310.1 [M+H]⁺;C₁₆H₁₅N₅O₂; ¹H NMR (400 MHz, DMSO-d₆): δ 7.97 (s, 1H), 7.24 (d, J=8.4Hz, 2H), 6.89 (dd, J=8.8 Hz, J=4.8 Hz, 2H), 6.36 (s, 2H), 4.84 (s, 2H),4.64 (d, J=2.4 Hz, 2H), 3.71 (s, 3H), 3.37 (s, 1H).

Step-4: 2-Amino-7-(prop-2-yn-1-yl)-7,9-dihydro-8H-purin-8-one (20)

Trifluoromethanesulfonic acid (21.84 g, 14.56 mol) was added to asuspension of2-amino-9-(4-methoxybenzyl)-7-(prop-2-yn-1-yl)-7,9-dihydro-8H-purin-8-one(19) (15.0 g, 4.854 mol) in trifluoroacetic acid (16.65 g, 14.56 mol) at0° C. under argon atmosphere and the resulting reaction mixture wasstirred at room temperature for 18 h. The reaction mixture was quenchedwith ice cold water, made basic with excess sat. NaHCO₃ solution undervigorous stirring and filtered. The residual solid was taken into ethylacetate, stirred for 30 min. and filtered. The solid residue was driedunder vacuum to afford2-amino-7-(prop-2-yn-1-yl)-7,9-dihydro-8H-purin-8-one (20) (6.50 g,70.85%) as a light yellow solid. ES+, m/z 190.1 [M+H]⁺; C₈H₇N₅O; ¹H NMR(400 MHz, DMSO-d₆): δ 11.32 (s, 1H), 7.57 (s, 1H), 5.60 (s, 2H), 4.46(s, 2H), 3.22 (s, 1H).

Step-5: N-(8-Oxo-7-(prop-2-yn-1-yl)-8,9-dihydro-7H-purin-2-yl)acetamide(21)

Acetic anhydride (4.86 mL, 4.76 mol) was added to a solution of2-amino-7-(prop-2-yn-1-yl)-7,9-dihydro-8H-purin-8-one (20) (6.0 g, 3.17mol) in DMF (60 mL) at room temperature under argon atmosphere and theresulting reaction mixture was stirred at 140° C. for 10 h. The reactionmixture was cooled to 0° C., whereupon a solid was formed under stirringfor 1 h. The product was filtered, washed with water and dried undervacuum to affordN-(8-oxo-7-(prop-2-yn-1-yl)-8,9-dihydro-7H-purin-2-yl)acetamide (21)(5.8 g, 79%) as a light yellow solid. ES+, m/z 232.1 [M+H]⁺; C₁₀H₉N₅O₂;¹H NMR (500 MHz, DMSO-d₆): δ 9.80 (s, 1H), 7.76 (s, 1H), 6.17 (s, 1H),4.53 (s, 2H), 3.24 (s, 1H), 2.11 (s, 3H).

Step-6:(S)-1-((2S,4R,5R)-5-(2-Acetamido-8-oxo-7-(prop-2-yn-1-yl)-7,8-dihydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)propylacetate (22)

Compound 6 was prepared according to the following 2 step procedure.

A stirred mixture ofN-(8-oxo-7-(prop-2-yn-1-yl)-8,9-dihydro-7H-purin-2-yl)acetamide (21)(300 mg, 1.298 mmol),(3R,5S)-5-((S)-1-acetoxypropyl)tetrahydrofuran-2,3-diyl diacetate (14S)(411 mg, 1.428 mmol), bis(trimethylsilyl)acetamide (0.87 mL, 3.894 mmol)in 1,2-dichloroethane (30 mL) was heated to 80° C. for 30 min underargon. The reaction mixture was cooled to RT and 1,2-dichloroethane wasremoved under vacuum. The residue was dissolved in ACN (30 mL) andTMSOTf (0.36 mL, 1.945 mmol) was added. The stirred reaction mixture washeated to 80° C. for 16 h. The reaction mixture was cooled to roomtemperature and concentrated under vacuum. The residue was diluted withaqueous sat. NaHCO₃ (50 mL) and extracted with EtOAc (3×50 mL). Thecombined EtOAc layer were washed with water (30 mL), brine (30 mL),dried over Na₂SO₄ and concentrated under vacuum. The crude compound waspurified by column chromatography over silica gel (100-200 mesh) using3% MeOH/DCM as eluent to afford 320 mg (53.6%) of(S)-1-((2S,4R,5R)-5-(2-acetamido-8-oxo-7-(prop-2-yn-1-yl)-7,8-dihydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)propylacetate (22) as a pale yellow solid. ES+, m/z 460.2 [M+H]⁺; C₂₁H₂₅N₅O₇.

Step-7:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-8H-purin-8-one,Compound 6

To a stirred solution of(S)-1-((2S,4R,5R)-5-(2-acetamido-8-oxo-7-(prop-2-yn-1-yl)-7,8-dihydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)propylacetate (22) (150 mg, 0.326 mmol) in MeOH (15 mL) was added K₂CO₃ (90mg, 0.653 mmol) at 0° C. Stirring was continued at RT for 16 h. Aceticacid (0.05 mL, 0.815 mmol) was added to this solution, stirred for 20min. and concentrated under reduced pressure at 30° C. The residue waspurified by normal phase GRACE flash chromatography (5% MeOH in DCM) toafford 50 mg (46%) of2-amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-8H-purin-8-one,Compound 6 as an off white solid. ES+, m/z 334.2 [M+H]⁺; C₁₅H₁₉N₅O₄: ¹HNMR (500 MHz, DMSO-d₆): δ 8.01 (s, 1H), 6.34 (brs, 2H), 5.60 (d, J=3.0Hz, 1H), 5.42 (d, J=4.5 Hz, 1H), 4.80 (t, J=3.5 Hz, 1H), 4.63 (d, J=2.5Hz, 2H), 4.54 (d, J=6.5 Hz, 1H), 4.03-4.01 (m, 1H), 3.39 (t, J=2.5 Hz,1H), 3.29-3.28 (m, 1H), 2.45-2.42 (m, 1H), 1.81-1.78 (m, 1H), 1.45-1.41(m, 1H), 1.28-1.26 (m, 1H), 0.87 (t, J=7.5 Hz, 3H).

Example 6:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(propa-1,2-dien-1-yl)-7,9-dihydro-8H-purin-8-one,Compound 7

To a stirred solution of(S)-1-((2S,4R,5R)-5-(2-acetamido-8-oxo-7-(prop-2-yn-1-yl)-7,8-dihydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)propylacetate (22) (150 mg, 0.326 mmol) in MeOH (15 mL) was added K₂CO₃ (135mg, 0.980 mmol) at 0° C. The reaction mixture was stirred at RT for 16h, whereupon it was concentrated under reduced pressure. The residue waspurified by normal phase GRACE flash chromatography (5% MeOH in DCM) andfurther purified by reverse phase GRACE flash chromatography (0.01%HCO₂H in ACN). The compound thus obtained was washed with acetonitrile(10 mL) and dried to afford 40 mg (36.6%) of2-amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(propa-1,2-dien-1-yl)-7,9-dihydro-8H-purin-8-one,Compound 7. ES+, m/z 334.1 [M+H]⁺; C₁₅H₁₉N₅O₄: ¹H NMR (500 MHz,DMSO-d₆): δ 8.12 (s, 1H), 7.20 (t, J=6.5 Hz, 1H), 6.47 (brs, 2H), 5.82(d, J=6.5 Hz, 2H), 5.63 (d, J=3.0 Hz, 1H), 5.42 (d, J=7.5 Hz, 1H),4.81-4.78 (m, 1H), 4.50 (d, J=6.5 Hz, 1H), 4.04-4.02 (m, 1H), 3.31-3.28(m, 1H), 2.50-2.42 (m, 1H), 1.79-1.78 (m, 1H), 1.47-1.39 (m, 1H),1.28-1.23 (m, 1H), 0.87 (t, J=7.5 Hz, 3H).

Example 7:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(propa-1,2-dien-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 8

To a stirred solution of(S)-1-((2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)propylacetate (7A) (200 mg, 0.421 mmol) in MeOH (10 mL) was added K₂CO₃ (290mg, 2.10 mmol) at 0° C. The reaction mixture was stirred at rt for 16 hand methanol was concentrated under reduced pressure at rt. The residueobtained was directly purified by GRACE reverse phase 0.1% FA:ACN(performed twice) and pure fraction was lyophilized to afford2-amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(propa-1,2-dien-1-yl)-7,9-dihydro-1H-purine-6,8-dioneas an off white solid. C₁₅H₁₉N₅O₅: ¹H NMR (500 MHz, DMSO-d₆): δ 10.96(brs, 1H), 7.18 (t, J=6.5 Hz, 1H), 6.60 (brs, 2H), 5.56 (d, J=3.0 Hz,1H), 5.51 (d, J=3.0 Hz, 2H), 5.45 (d, J=8.0 Hz, 1H), 4.74-4.72 (m, 1H),4.48 (d, J=6.5 Hz, 1H), 3.98 (q, J=3.0 Hz, 1H), 3.29-3.26 (m, 1H),2.36-2.33 (m, 1H), 1.76-1.73 (m, 1H), 1.39-1.38 (m, 1H), 1.27-1.24 (m,1H), 0.87 (t, J=7.5 Hz, 3H).

Example 8:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 9

Compound 9 was also synthesized according to the following multi-stepprocedure.

Step-1:(R)-1-((3aR,5S,6aR)-2,2-Dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethan-1-ol(15S)

To a stirred solution of(3aR,5S,6aR)-2,2-dimethyl-5-((R)-oxiran-2-yl)tetrahydrofuro[2,3-d][1,3]dioxole(9S) in dry THF (3 g, 15.9 mmol) under N₂ atmosphere was added LAH (1 Min THF, 53 mL, 159 mmol) at 0° C. After being stirred at 0° C. for 2hrs, the reaction mixture was quenched with saturated NH₄Cl solution (50mL). The organic layer was separated and the aqueous phase was extractedwith EtOAc (2×200 mL). The combined organic layer was dried over Na₂SO₄and concentrated in vacuum. The crude was purified by columnchromatography on silica gel (100-200 mesh, eluting with 40% EtOAc inpetroleum ether) to afford 2.7 g (89%) of(R)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethan-1-olas a colorless liquid. C₉H₁₆O₄: ¹H NMR (400 MHz, CDCl₃): δ 5.82 (d,J=3.6 Hz, 1H), 4.75 (t, J=4.0 Hz, 1H), 4.19-4.08 (m, 2H), 2.05 (brs,1H), 2.04-1.88 (m, 2H), 1.51 (s, 3H), 1.32 (s, 3H), 1.14 (d, J=6.4 Hz,3H).

Step-2:(S)-1-((3aR,5S,6aR)-2,2-Dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethyl4-nitrobenzoate (16S)

To a stirred solution of(R)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethan-1-ol(15S) (2.7 g, 39 mmol) in THE (30 mL) was added triphenylphosphine (7.5g, 28.7 mmol), 4-nitrobenzoic acid (4.7 g, 28.7 mmol) followed byaddition of diethylazodicarboxylate (4.5 mL, 28.7 mmol) dropwise at 0°C. under N₂ atmosphere. After being stirred at 25° C. for 10 h, themixture was quenched by addition of saturated NaHCO₃ solution (50 mL)and extracted with EtOAc (2×100 mL). The organic layers were combined,dried over Na₂SO₄ and concentrated in vacuum. The residue was purifiedby column chromatography on silica gel (100-200 mesh, eluting with 15%EtOAc in petroleum ether) to afford 3 g (62%) of(S)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethyl4-nitrobenzoate as a light yellow liquid. C₁₆H₁₉NO₇: ES+, m/z 338.2[M+H]⁺. ¹H NMR (400 MHz, CDCl₃): δ 8.30-8.20 (m, 4H), 5.86 (d, J=3.6 Hz,1H), 5.23 (quintet, J=6.4 Hz, 1H), 4.76 (t, J=4.4 Hz, 1H), 4.38 (ddd,J=10.8, 6.0, 4.8 Hz, 1H), 2.10 (dd, J=13.2, 4.4 Hz, 1H), 1.68 (m, 1H),1.63 (s, 3H), 1.41 (d, J=6.4 Hz, 3H), 1.33 (s, 3H).

Step-3:(S)-1-((3aR,5S,6aR)-2,2-Dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethan-1-ol(17S)

To a stirred solution of(R)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethan-1-ol(16S) (5.5 g, 16.3 mmol) in methanol (50 mL) was added K₂CO₃ (4.5 g,32.6 mmol). After being stirred at room temperature for 30 minutes, theresulted reaction mixture was filtered and the filtrate was concentratedin vacuum. The crude was purified by column chromatography on silica gel(100-200 mesh, eluting with 30% EtOAc in petroleum ether) to afford 2.7g (88%) of(S)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethan-1-olas a light yellow solid. C₉H₁₆O₄: ¹H NMR (400 MHz, CDCl₃): δ 5.81 (d,J=3.6 Hz, 1H), 4.76 (t, J=4.2 Hz, 1H), 4.12-4.05 (m, 1H), 3.68-3.65 (m,1H), 2.19 (d, J=4.0 Hz, 1H), 2.05-2.01 (m, 2H), 1.68-1.62 (m, 2H), 1.32(s, 3H), 1.20 (s, 3H).

Step-4:(S)-1-((3aR,5S,6aR)-2,2-Dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethylacetate (18S)

To a stirred solution of(S)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethan-1-ol(17S) (2.7 g, 14.0 mmol), TEA (3.9 mL, 28.0 mmol), DMAP (0.122 g, 2.0mmol) in anhydrous DCM (30 mL) was added acetic anhydride (2.1 mL, 21.0mmol). After being stirred at 25° C. for 10 h the reaction mixture wasquenched with saturated aq. NaHCO₃ solution (30 mL). The organic layerwas separated and the aqueous phase was extracted with CH₂C₂ (2×100 mL).The combined organic layers were dried over Na₂SO₄ and concentrated invacuum. The crude was purified by column chromatography on silica gel(100-200 mesh, eluting with 20% EtOAc in petroleum ether) to afford 3.2g (96%) of(S)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethylacetate as a colorless oil. C₁₁H₁₈O₅: ¹H NMR (400 MHz, CDCl₃): δ 5.83(d, J=4.0 Hz, 1H), 4.97-4.92 (m, 1H), 4.73 (t, J=3.2 Hz, 1H), 4.25-4.20(m, 1H), 2.07-2.01 (m, 4H), 1.67-1.60 (m, 1H), 1.52 (s, 3H), 1.32 (s,3H), 1.25 (d, J=4.0 Hz, 3H).

Step-5: (3R,5S)-5-((S)-1-Acetoxyethyl)tetrahydrofuran-2,3-diyl diacetate(19S)

To a solution of(S)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethylacetate (18S) (3.2 g, 13.9 mmol), acetic acid (7.9 mL, 139.1 mmol) andacetic anhydride (6.9 mL, 69.5 mmol) in anhydrous DCM (30 mL) was addedconcentrated H₂SO₄ (0.3 mL) at 0° C. After being stirred at 25° C. for 3hours, the reaction was quenched by addition of saturated aq. NaHCO₃solution (100 mL). The organic layer was separated and the aqueous phasewas extracted with EtOAc (2×100 mL). The combined organic layers wasdried over anhydrous Na₂SO₄ and concentrated in vacuum. The crudemixture was purified by column chromatography on silica gel (100-200mesh, eluting with 30% EtOAc in petroleum ether) to afford 1.3 g (47%)of (3R,5S)-5-((S)-1-acetoxypropyl)tetrahydrofuran-2,3-diyl diacetate asa colorless oil. C₁₂H₁₈O₇: ¹H NMR (500 MHz, CDCl₃): δ 6.39 (s, 1H), 5.18(d, J=3.6 Hz, 1H), 4.95-4.90 (m, 1H), 4.35-4.31 (m, 1H), 2.11-2.01 (m,11H), 1.21 (d, J=5.2 Hz, 3H).

Step-6:(S)-1-((2S,4R,5R)-5-(2-Acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)ethylacetate (23)

N-(6,8-Dioxo-7-(prop-2-yn-1-yl)-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide(6) (200 mg, 0.8 mmol)(3R,5S)-5-((S)-1-acetoxypropyl)tetrahydrofuran-2,3-diyl diacetate (19S)(265 mg, 0.96 mmol), BSA (0.61 mL, 2.4 mmol) were dissolved in1,2-dichloroethane (20 mL) and the resulting reaction mixture wasstirred at 80° C. for 30 min under argon. The reaction mixture wasallowed to warm to RT and 1,2-dichloro ethane was removed by vacuum. Theresidue was re-dissolved in ACN (20 mL) followed by addition of TMSOTf(0.22 mL, 1.2 mmol). The reaction mixture was heated at 80° C. for 16 h.Then the reaction mixture was cooled to room temperature andconcentrated under vacuum and the residue was diluted with aq·NaHCO₃ (50mL) and extracted with EtOAc (3×50 mL). The combined EtOAc layer waswashed with water (30 mL), brine (30 mL), dried over anhydrous Na₂SO₄and concentrated under vacuum. The crude compound was purified by GRACE(80% EtOAc in pet ether) to afford 200 mg (53%) of(S)-1-((2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)ethylacetate as an off-white solid. C₂₀H₂₃N₅O₈: ES+, m/z 462.2 [M+H]⁺.

Step-6:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 9

To a solution of(S)-1-((2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)ethylacetate (23) (200 mg, 0.43 mmol) in MeOH (10 mL) was added K₂CO₃ (59.6mg, 0.43 mmol) at 0° C. The resultant reaction mixture was stirred at RTfor 16 h. Then methanol was concentrated under reduced pressure at RTand the residue obtained was purified by Prep-HPLC. Upon lyophilizationof the pure fractions afforded 35 mg (24%) of2-amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 9 as an off white solid. C₁₄H₁₇N₅O₅: ES+, m/z 336.1 [M+H]⁺; ¹HNMR (400 MHz, DMSO-d₆): δ 10.93 (brs, 1H), 6.54 (brs, 2H), 5.22 (d,J=4.0 Hz, 1H), 5.39 (d, J=2.8 Hz, 1H), 5.39 (d, J=4.4 Hz, 1H), 4.75-4.71(m, 1H), 4.63-4.57 (m, 2H), 3.94-3.88 (m, 1H), 3.58-3.54 (m, 1H), 3.22(s, 1H), 2.38-2.33 (m, 1H), 1.75-1.70 (m, 1H), 1.06 (d, J=6.4 Hz, 3H).

Example 9: Compounds 10 and 112-Amino-9-((2R,3R,5S)-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 10

2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 11

Compounds 10 and 11 were prepared according to the following multi-stepprocedures.

Step-1:1-((3aR,5S,6aR)-2,2-Dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)-2,2,2-trifluoroethan-1-ol(20S)

To a stirred solution of(3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxole-5-carbaldehyde(4S) (4.2 g, 24.41 mmol) in anhydrous dichloromethane (60 mL) was cooledto 0° C. and trifluoromethyltrimethylsilane (3.81 g, 26.86 mmol) wasadded followed by addition of a catalytic amount oftetra-n-butylammonium difluorotriphenylstannate (1.53 g, 2.44 mmol). Thereaction mixture was warmed to room temperature and stirred for 10 h.The reaction mixture was then treated with one equivalent of TBAF (1M inTHF) (24.4 mL) and stirred for 1 h and was then quenched with aqueousNH₄Cl and dichloromethane. The organic layer was separated, dried overNa₂SO₄ and concentrated in vacuum. The crude product was purified bycolumn chromatography on silica gel (100-200 mesh, eluting with 30%EtOAc in petroleum ether) to afford1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)-2,2,2-trifluoroethan-1-ol(20S) (2 g, 33%, as a diastereomeric mixture) as a colourless oil.C₉H₁₃F₃O₄ (diastereomeric mixture): ¹H NMR (400 MHz, CDCl₃): δ 5.86-5.81(m, 2H), 4.79-4.75 (m, 2H), 4.50-4.43 (m, 2H), 4.38-4.34 (m, 1H),3.88-3.83 (m, 1H), 2.92 (d, J=9.2 Hz, 1H), 2.79 (bs, 1H), 2.20-2.15 (m,1H), 2.09-2.06 (m, 2H), 1.98-1.91 (m, 1H), 1.52 (s, 6H), 1.34 (s, 6H).

Step-2:1-((3aR,5S,6aR)-2,2-Dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)-2,2,2-trifluoroethylacetate (21S)

To a stirred solution of1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)-2,2,2-trifluoroethan-1-ol(20S) (2 g, 8.26 mmol), TEA (2.37 mL, 16.52 mmol), DMAP (0.201 g, 1.65mmol) in anhydrous DCM (30 mL) was added acetic anhydride (1.22 mL,12.39 mmol). After being stirred at 25° C. for 10 h, the reaction wasquenched by saturated aq. NaHCO₃ solution (50 mL). The organic layer wasseparated and the aqueous phase was extracted with DCM (2×50 mL). Thecombined organic layers were dried over anhydrous Na₂SO₄ andconcentrated in vacuum. The crude mixture was purified by columnchromatography on silica gel (100-200 mesh, eluting with 30% EtOAc inpetroleum ether) to afford1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)-2,2,2-trifluoroethylacetate (21S) (1.6 g, 69% as a diastereomeric mixture) as a colourlessoil. C₁₁H₁₅F₃O₅ (as a diastereomeric mixture): ¹H NMR (500 MHz, CDCl₃):δ 5.82 (d, J=3.5 Hz, 1H), 4.77 (d, J=4.0 Hz, 1H), 5.67-5.65 (m, 1H),5.36-5.33 (m, 1H), 4.76-4.74 (m, 2H), 4.53-4.44 (m, 2H), 2.21-2.20 (m,1H), 2.20 (s, 3H), 2.16 (s, 3H), 2.15-2.12 (m, 1H), 1.98-1.90 (m, 1H),1.75-1.67 (m, 1H), 1.52 (s, 6H), 1.34 (s, 6H).

Step-3:(2S,3R,5S)-5-(1-Acetoxy-2,2,2-trifluoroethyl)tetrahydrofuran-2,3-diyldiacetate (22S)

To a solution of1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)-2,2,2-trifluoroethylacetate (1.6 g, 4.87 mmol), acetic acid (2.92 mL, 48.7 mmol) and aceticanhydride (2.32 mL, 24.39 mmol) in anhydrous DCM (30 mL) was addedconcentrated H₂SO₄ (0.1 mL) at 0° C. After being stirred at 25° C. for 3hours, the reaction was quenched by addition of saturated aq·NaHCO₃solution (100 mL). The organic layer was separated and the aqueous phasewas extracted with DCM (2×70 mL). The combined organic layers were driedover anhydrous Na₂SO₄ and concentrated in vacuum. The crude was purifiedby column chromatography on silica gel (100-200 mesh, eluting with 20%EtOAc in petroleum ether) to afford(2S,3R,5S)-5-(1-acetoxy-2,2,2-trifluoroethyl)tetrahydrofuran-2,3-diyldiacetate (22S) (700 mg, 38%, as a diastereomeric mixture) as acolourless oil. C₁₂H₁₅F₃O₇ (as a diastereomeric mixture): ¹H NMR (400MHz, CDCl₃): δ 6.14 (d, J=9.6 Hz, 2H), 5.61-5.58 (m, 1H), 5.33-5.27 (m,1H), 5.22-5.19 (m, 2H), 4.71-4.66 (m, 1H), 4.61-4.55 (m, 1H), 2.44-2.37(m, 1H), 2.36-2.20 (s, 2H), 2.19 (s, 3H), 2.17 (s, 3H), 2.12-2.09 (m,4H), 2.06 (s, 9H).

Step-4:(R)-1-((2S,4R,5R)-5-(2-Acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2,2,2-trifluoroethylacetate (24A) and(S)-1-((2S,4R,5R)-5-(2-Acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2,2,2-trifluoroethylacetate (24B)

ToN-(6,8-dioxo-7-(Prop-2-yn-1-yl)-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide(6) (400 mg, 1.61 mmol),(2S,3R,5S)-5-(1-acetoxy-2,2,2-trifluoroethyl)tetrahydrofuran-2,3-diyldiacetate (22S) (637 mg, 1.94 mmol) dissolved in 1,2-dichloroethane (20mL) was added BSA (1.2 mL, 4.85 mmol). The resulting reaction mixturewas stirred at 80° C. for 30 min under argon and then cooled to roomtemperature and 1,2-dichloroethane was removed under vacuum. The residuewas dissolved in acetonitrile (20 mL) followed by the addition of TMSOTf(0.44 mL, 2.42 mmol). The reaction mixture was heated at 80° C. for 16h, cooled to room temperature and concentrated under vacuum and to theresidue obtained was added aq. NaHCO₃ (50 mL) and extracted with EtOAc(3×50 mL). The combined EtOAc layer was washed with water (30 mL), brine(30 mL), dried over Na₂SO₄ and concentrated under vacuum. The crudecompound was purified by GRACE flash chromatography (using 80% EtOAc inpet ether as eluent) to afford 250 mg (LC/MS: 55%-25% of diastereomericmixture) of(R,S)-1-((2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2,2,2-trifluoroethylacetate (24A, 24B) as a brown solid. Further purification by Prep-HPLC(X-SELECT-C18 (250*19), 5 u Mobile phase: 10 mM ammonium bicarbonate inH₂O:MeCN GRADIENT: (T % B):—0/20, 8/58, 16/98, 16.1/20, 19/20 Flow Rate:18 ml/min Diluent: MeCN+H₂O+THF) gave 130 mg of(R)-1-((2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2,2,2-trifluoroethylacetate (24A); C₂₀H₂₀F₃N₅O₈: ES+, m/z 516.2 [M+H]⁺ and 80 mg(S)-1-((2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2,2,2-trifluoroethylacetate (24B); C₂₀H₂₀F₃N₅O₈: ES+, m/z 516.1 [M+H]⁺.

Step-5:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 10

To a solution of(R)-1-((2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2,2,2-trifluoroethylacetate (24A) (130 mg, 0.252 mmol) in MeOH (20 mL) was added K₂CO₃ (34mg, 0.252 mmol) at 0° C. and the reaction mixture was stirred at RT for16 h. Methanol was removed under reduced pressure at 30° C. The residuewas directly purified by a reverse phase GRACE flash chromatography(using 10 mM ammonium bicarbonate in H₂O as eluent). Lyophilization ofthe pure fractions afforded 30 mg (50%) of2-amino-9-((2R,3R,5S)-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 10 as a white solid. C₁₄H₁₄F₃N₅O₅: ES−, m/z 388.0 [M−H]⁻. ¹HNMR (400 MHz, DMSO-d₆): δ 11.21 (brs, 1H), 6.62 (brs, 2H), 6.53 (d,J=6.4 Hz, 1H), 5.58 (d, J=6.4 Hz, 1H), 5.10 (d, J=4.4 Hz, 1H),4.833-4.79 (m, 1H), 4.59 (d, J=2.0 Hz, 2H), 4.26 (q, J=14.4 Hz, 14.8 Hz,1H), 4.13 (q, J=14.0 Hz, 14.0 Hz, 1H), 3.21 (t, J=2.4 Hz, 1H), 2.72-2.65(m, 1H), 1.96-1.90 (m, 1H).

Step-6:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 11

To a solution of(S)-1-((2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2,2,2-trifluoroethylacetate (24B) (80 mg, 0.155 mmol) in MeOH (20 mL) was added K₂CO₃ (21mg, 0.155 mmol) at 0° C. and the reaction mixture was stirred at RT for16 h. Methanol was removed under reduced pressure at 30° C. and theresidue obtained was directly purified by reverse phase GRACE flashchromatography (using 10 mM ammonium bicarbonate in H₂O as eluent).Lyophilization of the pure fractions afforded 30 mg (81%) of2-amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 11 as a white solid. C₁₄H₁₄F₃N₅O₅: ES+, m/z 390.1 [M+H]⁺. ¹HNMR (400 MHz, DMSO-d₆): δ 11.02 (brs, 1H), 6.57 (brs, 2H), 6.30 (d,J=8.4 Hz, 1H), 5.57-5.54 (m, 2H), 4.76-4.72 (m, 1H), 4.60 (d, J=2.4 Hz,2H), 4.34-4.29 (m, 1H), 4.05-4.00 (m, 1H), 3.24 (t, J=2.4 Hz, 1H),2.56-2.52 (m, 1H), 1.97-1.91 (m, 1H).

Example 10: Compounds 12 and 132-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((R)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 12

2-Amino-9-((2R,3S,4R,5S)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 13

Compounds 12 and 13 were prepared according to the following multi-stepprocedures.

The synthesis of (27S) was carried out according to the proceduresdescribed in U.S. Pat. No. 9,708,607B2.

Step-1:(3aR,5R,6aS)-5-((R)-2,2-Dimethyl-1,3-dioxolan-4-yl)-2,2-dimethyldihydrofuro[2,3-d][1,3]dioxol-6(5H)-one(23S)

To a stirred solution of(3aR,5S,6S,6aR)-5-((R)-2,2-dimethyl-1,3-dioxolan-4-yl)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-6-ol[582-52-5] (2 g, 7.68 mmol) and Ac₂O (2 mL) in CH₂Cl₂ (20 mL) was addedpyridinium dichromate (3.5 g, 9.30 mmol). The reaction mixture stirredat room temperature for 16 h. At this time the reaction mixture wasconcentrated under vacuum and EtOAc (3×100 mL) was added with stirring.The residual mixture was filtered through silica-gel and concentrated invacuum. The crude product was used in next step without furtherpurification, to afford (1.1 g, 55.44%) of(3aR,5R,6aS)-5-((R)-2,2-dimethyl-1,3-dioxolan-4-yl)-2,2-dimethyldihydrofuro[2,3-d][1,3]dioxol-6(5H)-one(23S) [2847-00-9] as an off white solid. C₁₂H₁₈O₆: ¹H NMR (400 MHz,CDCl₃): δ 6.14 (d, J=4.8 Hz, 1H), 4.39-4.35 (m, 3H), 4.02 (d, J=0.8 Hz,1H), 2.10 (s, 1H), 1.49 (s, 3H), 1.36 (s, 3H), 1.34 (s, 6H).

Step-2:(3aR,5S,6R,6aR)-5-((R)-2,2-Dimethyl-1,3-dioxolan-4-yl)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-6-ol(24S)

To a solution of(3aR,5R,6aS)-5-((R)-2,2-dimethyl-1,3-dioxolan-4-yl)-2,2-dimethyldihydrofuro[2,3-d][1,3]dioxol-6(5H)-one(23S) (1.9 g, 7.36 mmol) in EtOH:water (10 mL: 3 mL) was added NaBH₄(292 mg, 8.83 mmol). The reaction mixture stirred at room temperaturefor 16 h and concentrated under vacuum. To the residue was added EtOAc(3×100 mL) with stirring. The mixture was then passed through silica-geland concentrated in vacuum. The crude product was used in next stepwithout any further purification to afford (1 g, 52.2%) of(3aR,5S,6R,6aR)-5-((R)-2,2-dimethyl-1,3-dioxolan-4-yl)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-6-ol(24S) [2595-05-3] as an off white solid. C₁₂H₂₀O₆: ¹H NMR (500 MHz,CDCl₃): δ 5.65 (d, J=3.5 Hz, 1H), 5.09 (d, J=7.0 Hz, 1H), 4.46 (t, J=4.0Hz, 1H), 4.24-4.21 (m, 1H), 3.93 (t, J=8.0 Hz, 1H), 3.85-3.73 (m, 3H),1.44 (s, 3H), 1.32 (s, 3H), 1.27 (s, 3H), 1.26 (s, 3H).

Step-3:(3aR,5R,6S,6aS)-5-((R)-2,2-Dimethyl-1,3-dioxolan-4-yl)-6-fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxole(25S)

To a solution of(3aR,5S,6R,6aR)-5-((R)-2,2-dimethyl-1,3-dioxolan-4-yl)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-6-ol(24S) (22 g, 84.61 mmol) in pyridine (10 ml, 126.92 mmol) and anhydrousCH₂Cl₂ (200 mL) was slowly added DAST (16.8 mL, 126.92 mmol). Thereaction mixture and stirred at room temperature for 48 h, cooled to 0°C. and poured into saturated cold aqueous NaHCO₃ (100 mL). The aqueouslayer was extracted with CH₂Cl₂ (3×300 mL). The combined organic layerswere dried over Na₂SO₄, filtered and evaporated under reduced pressure.The crude residue was purified by column chromatography (silica gel;hexane:ethyl acetate 7:3) to afford 15 g (67.7%) of(3aR,5R,6S,6aS)-5-((R)-2,2-dimethyl-1,3-dioxolan-4-yl)-6-fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxole(25S) [14049-05-9] as a thick yellow mass. C₁₂H₁₉FO₅: ¹H NMR (400 MHz,CDCl₃): δ 5.95 (d, J=3.6 Hz, 1H), 5.07 (dd, J=2.0 Hz, 1H), 4.71-4.68(dd, J=4 Hz, 1H), 4.31-4.26 (m, 1H), 4.16-4.10 (m, 3H), 1.50 (s, 3H),1.45 (s, 3H), 1.36 (s, 3H), 1.32 (s, 3H).

Step-4:(R)-1-((3aR,5R,6S,6aS)-6-Fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethane-1,2-diol(26S)

A solution of(3aR,5R,6S,6aS)-5-((R)-2,2-dimethyl-1,3-dioxolan-4-yl)-6-fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxole(25S) (2.0 g, 7.66 mmol) in 60% AcOH/water (12 mL) was stirred at roomtemperature for 24 h. The mixture was concentrated under vacuum toafford 1.6 g (94%) of(R)-1-((3aR,5R,6S,6aS)-6-fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethane-1,2-diol(26S) [18530-81-9] as a colorless oil. The crude product was usedwithout purification. C₉H₁₅FO: ¹H NMR (400 MHz, DMSO-d₆): δ 5.94 (d,J=3.6 Hz, 1H), 5.01 (dd, J=30.0, 2.0 Hz, 1H), 4.72 (dd, J=10.8, 4.0 Hz,1H), 4.99 (ddd, 1H, J=30.0, 9.2, 2.0 Hz), 3.60-3.54 (m, 2H), 3.40-3.30(m, 1H), 1.90 (s, 2H), 1.39 (s, 3H), 1.26 (s, 3H).

Step-5:(3aR,5R,6S,6aS)-6-Fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxole-5-carbaldehyde(27S)

To a solution of(R)-1-((3aR,5R,6S,6aS)-6-fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethane-1,2-diol(26S) (2 g, 9.0 mmol) in methanol (20 mL) cooled in an ice bath wasadded sodium metaperiodate (2.3 g, 10.81 mmol). After being stirred atroom temperature for 16 h, the resulting suspension was filtered. Thefiltrate was concentrated in vacuum. The residue was purified by columnchromatography on silica gel (EtOAc) to afford 1.4 g (81.53%) of(3aR,5R,6S,6aS)-6-fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxole-5-carbaldehyde(27S) [70722-99-5] as an colourless oil, C₈H₁₁FO₄, and was used in nextstep without further purification.

Step-6:1-((3aR,5R,6S,6aS)-6-Fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propan-1-ol(28S)

To a solution of(3aR,5R,6S,6aS)-6-fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxole-5-carbaldehyde(27S) (1 g, 5.26 mmol) in THE (20 mL) was added ethyl magnesium bromide(1M in THF, 5.26 mL, 5.26 mmol) at −20° C. under argon. After beingstirred at room temperature for 16 h the reaction mixture was quenchedby saturated NH₄Cl solution and extracted with EtOAc (3×50 mL). Thecombined organic layers were filtered and concentrated in vacuum. Theresidue was purified by column chromatography on silica gel (elutingwith 1:4 EtOAc in Pet-ether) to afford 800 mg (69.14%) of adiastereomeric mixture of1-((3aR,5R,6S,6aS)-6-fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propan-1-ol(28S) as a colorless oil and used without further purification.

Step-7: 1-((3aR,5R,6S,6aS)-6-Fluoro-2,2-dimethyltetrahydrofuro[2,3-d][,3]dioxol-5-yl)propyl acetate (29S)

To a stirred solution of1-((3aR,5R,6S,6aS)-6-fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propan-1-ol(28S) (1.2 g, 5.42 mmol), TEA (1.52 mL, 10.85 mmol) and DMAP (133 mg,1.08 mmol) in anhydrous DCM (20 mL) was added acetic anhydride (830 mg,8.14 mmol). The resultant reaction mixture was stirred at 22° C. for 18h, then quenched with saturated aq. NaHCO₃ solution (20 mL). The organiclayer was separated and the aqueous phase was extracted with DCM (2×50mL). The combined organic layers were dried over Na₂SO₄, filtered andconcentrated in vacuum. The crude product was purified by columnchromatography on silica gel (100-200 mesh, 20% EtOAc in petroleumether) to afford 700 mg (49%) of1-((3aR,5R,6S,6aS)-6-fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propylacetate (29S) as a colorless oil (diastereomeric mixture). C₁₂H₁₉FO₅: ¹HNMR (400 MHz, CDCl₃): δ 5.96 (d, J=3.6 Hz, 1H), 5.13-5.07 (m, 1H), 4.90(dd, J=50.0, 2.4 Hz, 1H), 4.68 (dd, J=10.6, 4.0 Hz, 1H), 4.24-4.01 (m,2H), 2.04 (s, 3H), 1.92-1.85 (m, 1H), 1.71-1.64 (m, 1H), 1.51 (s, 3H),1.32 (s, 3H), 0.95 (t, J=7.6 Hz, 3H).

Step-8: (3S,4S,5R)-5-(1-Acetoxypropyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate (30S)

To a stirred solution of1-((3aR,5R,6S,6aS)-6-fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propylacetate (29S) (600 mg, 2.28 mmol), acetic acid (1.3 mL, 22.81 mmol) andacetic anhydride (1.08 mL, 11.46 mmol) in anhydrous DCM (10 mL) wasadded concentrated H₂SO₄ (0.10 mL) at 0° C. After stirring at RT for 3hours, the reaction mixture was quenched by addition of saturated aq.NaHCO₃ solution (10 mL). The organic layer was separated and the aqueousphase was extracted with DCM (2×50 mL). The combined organic layers weredried over Na₂SO₄ and concentrated in vacuum. The crude product waspurified by column chromatography on silica gel (100-200 mesh, 30% EtOAcin petroleum ether) to afford a mixture of diastereomers (300 mg,42.85%) of(3S,4S,5R)-5-(1-acetoxypropyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate (30S) as a colorless oil. C₁₃H₁₉FO₇: ¹H NMR (400 MHz, CDCl₃):δ 6.13 (s, 1H), 5.30-5.15 (m, 1H), 5.12-5.04 (m, 1H), 4.37-4.29 (m, 2H),4.44-4.34 (m, 1H), 2.10-2.08 (m, 9H), 1.88-1.69 (m, 1H), 1.68-1.59 (m,1H), 0.95-0.88 (m, 3H).

Step-9:(R)-1-((2R,3S,4S,5R)-5-(2-Acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxy-3-fluorotetrahydrofuran-2-yl)propylacetate (25A) and(S)-1-((2R,3S,4S,5R)-5-(2-Acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxy-3-fluorotetrahydrofuran-2-yl)propylacetate (25B)

ToN-(6,8-dioxo-7-(prop-2-yn-1-yl)-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide(6) (340 mg, 1.28 mmol),(3S,4S,5R)-5-(1-acetoxypropyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate (30S) (504 mg, 1.66 mmol) dissolved in 1,2-dichloroethane (10mL) was added bis(trimethylsilyl)acetamide (77 mg, 3.84 mmol). Thereaction mixture was stirred at 80° C. for 30 min under argon, cooled toRT whereupon 1,2-dichloroethane was removed under vacuum. The residuewas then dissolved in MeCN (20 mL) followed by addition of TMSOTf (0.43mL, 1.92 mmol). The reaction mixture was heated at 80° C. for 16 h,cooled to room temperature and concentrated under vacuum. The residuewas diluted with aq. NaHCO₃ (50 mL) and extracted with EtOAc (3×50 mL).The combined EtOAc layer was washed with water (30 mL), brine (30 mL),dried over Na₂SO₄, filtered and concentrated under vacuum. The crudecompound was purified by Prep HPLC using KROMOSIL C18 column (150*25MM), 10 u Mobile phase: 0.1% HCO₂H in H₂O:MeOH Gradient: (T % B): —0/50,1/50, 8/70, 10/70, 10.1/98, 13/98, 13.1/50, 15/50 Flow Rate: 20 mL/min;Diluent: MeCN+H₂O+THF to afford 50 mg of(R)-1-((2R,3S,4S,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxy-3-fluorotetrahydrofuran-2-yl)propylacetate (25A); C₂₁H₂₄FN₅O₈: ES+, m/z 494.2 [M+H]⁺ and 50 mg of(S)-1-((2R,3S,4S,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxy-3-fluorotetrahydrofuran-2-yl)propylacetate (25B); C₂₁H₂₄FN₅O₈: ES+, m/z 494.2 [M+H]⁺ both as a yellowsolids.

Step-10:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((R)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-H-purine-6,8-dione,Compound 12

To a solution of(R)-1-((2R,3S,4S,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxy-3-fluorotetrahydrofuran-2-yl)propylacetate (25A) (50 mg, 0.10 mmol) in MeOH (4 mL) was added K₂CO₃ (14 mg,0.10 mmol) at 0° C. The reaction mixture was stirred at RT for 16 h.Methanol was removed under reduced pressure at 30° C. The residue wasdirectly purified by a reverse phase GRACE flash chromatography (using0.01% aq. HCO₂H and MeCN as eluent). The pure fractions were lyophilizedto afford 20 mg (53.7%) of2-amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((R)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 12 as a white solid. C₁₅H₁₈FN₅O₅: ES+, m/z 368.2 [M+H]⁺. ¹H NMR(400 MHz, DMSO-d₆): δ 11.04 (brs, 1H), 6.63 (brs, 2H), 5.91 (d, J=5.6Hz, 1H), 5.33-5.32 (m, 1H), 5.28-5.25 (m, 1H), 5.00 (d, J=3.6 Hz, 1H),4.85 (d, J=6.0 Hz, 1H), 4.59 (d, J=2.4 Hz, 2H), 3.71-3.60 (m, 2H),3.24-3.23 (t, J=2.4 Hz, 1H), 1.59-1.53 (m, 1H), 1.32-1.25 (m, 1H), 0.88(t, J=7.2 Hz, 3H).

Step-11:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 13

To a solution of(S)-1-((2R,3S,4S,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxy-3-fluorotetrahydrofuran-2-yl)propylacetate (25B) (50 mg, 0.11 mmol) in MeOH (4 mL) was added K₂CO₃ (16 mg,0.11 mmol) at 0° C. The reaction mixture was stirred at RT for 16 hwhereupon methanol was removed under reduced pressure at 30° C. Theresidue was purified by reverse phase GRACE flash chromatography (using0.01% aq. HCO₂H and MeCN as eluent). The pure fractions were lyophilizedto afford (15 mg, 40.3%) of2-amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 13 as a white solid. C₁₅H₁₈FN₅O₅: ES+, m/z 368.1 [M+H]⁺. ¹H NMR(400 MHz, DMSO-d₆): δ 11.0 (brs, 1H), 6.58 (brs, 2H), 5.94 (d, J=5.6 Hz,1H), 5.36 (m, 1H), 5.29 (m, 1H), 4.97 (ddd, 1H, J=53.7, 4.6, 2.2 Hz,1H), 4.82 (d, J=6.8 Hz, 1H), 4.61 (d, J=2.4 Hz, 2H), 3.80 (ddd, J=23.6,7.0, 4.6 Hz, 1H), 3.54 (m, 1H), 3.25 (t, J=2.4 Hz, 1H), 1.49 (m, 1H),1.33 (m, 1H), 0.92 (t, J=7.4 Hz, 3H).

Alternative Synthetic Procedure for Compound 13

Example 11:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 13

Compound 13 was also prepared according to the following stereoselectivemulti-step synthesis.

Step-1:(R)-2-((3aR,5R,6S,6aS)-6-Fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)-2-hydroxyethyl4-methylbenzenesulfonate (31S)

To a solution of(R)-1-((3aR,5R,6S,6aS)-6-fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethane-1,2-diol(26S) (4 g, 18.01 mmol) in dry pyridine (40 mL) was addedp-toluenesulfonyl chloride (4.79 g, 25.22 mmol) at 0° C. After stirringthe reaction mixture at room temperature for 12 h, pyridine was removedunder vacuum. The residue was diluted with water (100 mL) and extractedwith EtOAc (2×200 mL). The combined EtOAc layer was dried over Na₂SO₄and concentrated. The residue was purified by column chromatography onsilica gel (100-200 mesh, eluting with 25% EtOAc in Pet-ether) to afford(2 g, 29.5%) of(R)-2-((3aR,5R,6S,6aS)-6-fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)-2-hydroxyethyl4-methylbenzenesulfonate (31S) as a light yellow oil. C₁₆H₂₁FO₇S: ES+,m/z 394.2 [M+H₂O]⁺. ¹H NMR (400 MHz, CDCl₃): δ 7.81 (d, J=6.4 Hz, 2H),7.37 (d, J=8.00 Hz, 2H), 5.90 (d, J=3.6 Hz, 1H), 5.13 (dd, J=2.4 Hz,1H), 4.69 (dd, J=3.6 Hz, 1H), 4.32 (d, J=7.2 Hz, 1H), 4.13-4.04 (m, 3H),2.47 (d, J=4.8 Hz, 1H), 2.45 (s, 3H), 1.46 (s, 3H), 1.31 (s, 3H).

Step-2:(3aR,5R,6S,6aS)-6-Fluoro-2,2-dimethyl-5-((R)-oxiran-2-yl)tetrahydrofuro[2,3-d][1,3]dioxole(32S)

To a solution of(R)-2-((3aR,5R,6S,6aS)-6-fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)-2-hydroxyethyl4-methylbenzenesulfonate (31S) (2 g, 5.31 mmol) in anhydrous THE (10 mL)cooled at −78° C. was added potassium bis(trimethylsilyl)amide (6.43 mL,6.43 mmol, 1 M in THF) under N₂ atmosphere. After being stirred at −78°C. for 1 h, the reaction mixture was poured into a saturated NH₄Clsolution. The organic layer was separated and the aqueous phase wasextracted with EtOAc (2×100 mL). The combined organic layer was driedover Na₂SO₄, filtered and concentrated in vacuum. The crude product waspurified by column chromatography over silica gel (100-200 mesh; 25%EtOAc in petroleum ether) to afford (900 mg, 82.9%) of(3aR,5R,6S,6aS)-6-fluoro-2,2-dimethyl-5-((R)-oxiran-2-yl)tetrahydrofuro[2,3-d][1,3]dioxole(32) as a light yellow oil. C₉H₁₃FO₄: ¹H NMR: (400 MHz, CDCl₃): δ 6.00(d, J=3.6 Hz, 1H), 5.06 (dd, J=50.0, 2.0 Hz, 1H), 4.73 (dd, J=10.8, 3.6Hz, 1H), 3.80 (ddd, J=28.6, 6.8, 2.2 Hz, 1H), 3.22 (m, 1H), 2.93 (dd,J=5.0, 3.6 Hz, 1H), 2.80 (dd, J=5.0, 2.6 Hz, 1H), 1.45 (s, 3H), 1.33 (s,3H).

Step-3:(R)-1-((3aR,5R,6S,6aS)-6-Fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propan-1-ol(33S)

To a stirred suspension of CuI (186 mg, 0.980 mmol) in dry THE (20 mL)under N₂ atmosphere was added methylmagnesium bromide (1.0 M in diethylether, 14.7 mL, 14.70 mmol) at −78° C. After being stirred at −78° C.for 1 hour a solution of(3aR,5R,6S,6aS)-6-fluoro-2,2-dimethyl-5-((R)-oxiran-2-yl)tetrahydrofuro[2,3-d][1,3]dioxole(32S) (1.0 g, 4.90 mmol) in THE (10 mL) was added and stirred at −78° C.for an additional 2 hours. The reaction mixture was poured into asaturated NH₄Cl solution (200 mL), the organic layer was separated andthe aqueous phase was extracted with EtOAc (2×200 mL). The combinedorganic layers were dried over Na₂SO₄, filtered and concentrated invacuum. The crude product was purified by column chromatography onsilica gel (100-200 mesh, 30% EtOAc in petroleum ether) to afford 1.0 g(92.3%) of(R)-1-((3aR,5R,6S,6aS)-6-fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propan-1-ol(33S) as a light yellow oil. C₁₀H₁₇FO₄: ¹H NMR (400 MHz, CDCl₃): δ 5.98(d, J=3.6 Hz, 1H), 5.08 (dd, J=50.0, 2.4 Hz, 1H), 4.69 (dd, J=11.2, 3.6Hz, 1H), 4.01 (dd, J=29.8, 2.4 Hz, 1H), 3.85 (m, 1H), 1.86-1.80 (m, 1H),1.75 (d, J=6.0 Hz, 1H), 1.52 (s, 3H), 1.32 (s, 3H), 1.05 (t, J=7.2 Hz,3H).

Step-4:(S)-1-((3aR,5R,6S,6aS)-6-Fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propyl4-nitrobenzoate (34S)

To a stirred solution of(R)-1-((3aR,5R,6S,6aS)-6-fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propan-1-ol(33S) (1.0 g, 4.52 mmol), triphenylphosphine (2.3 g, 9.04 mmol),4-nitrobenzoic acid (1.51 g, 9.04 mmol) in THF (240 mL) was addeddiethylazodicarboxylate (1.57 mL, 9.04 mmol) dropwise at 0° C. under N₂atm. After being stirred at RT for 10 h, the mixture was quenched byaddition of a saturated NaHCO₃ solution (50 mL) and extracted with EtOAc(2×50 mL). The organic layers were combined, dried over Na₂SO₄, filteredand concentrated in vacuum. The residue was purified by columnchromatography on silica gel (100-200 mesh, 15% EtOAc in pet ether) toafford (650 mg, 38.9%) of(S)-1-((3aR,5R,6S,6aS)-6-fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propyl4-nitrobenzoate (34S) as a light yellow solid. C₁₇H₂₀FNO₇: ES+, m/z370.2 [M+H]⁺. ¹H NMR (400 MHz, CDCl₃): δ 8.30-8.21 (m, 4H), 6.00 (d,J=3.6 Hz, 1H), 5.51 (m, 1H), 4.97 (dd, J=50.0, 2.4 Hz, 1H), 4.73 (dd,J=11.4, 3.6 Hz, 1H), 4.35 (ddd, J=29.2, 8.2, 2.4 Hz, 1H), 1.89-1.80 (m,2H), 1.51 (s, 3H), 1.33 (s, 3H), 1.03 (t, J=7.2 Hz, 3H).

Step-5:(S)-1-((3aR,5R,6S,6aS)-6-Fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propan-1-ol(35S)

To a stirred solution of(S)-1-((3aR,5R,6S,6aS)-6-fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propyl4-nitrobenzoate (34S) (650 mg, 1.76 mmol) in methanol (10 mL) was addedK₂CO₃ (486 mg, 3.52 mmol). After being stirred at room temperature for 3h, the resultant reaction mixture was filtered and the filtrate wasconcentrated in vacuum. The crude material was purified by columnchromatography on silica gel (100-200 mesh, 30% EtOAc in petroleumether) to afford (389 mg, 100%) of(S)-1-((3aR,5R,6S,6aS)-6-fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propan-1-ol(35S) as a light yellow oil. C₁₀H₁₇FO₄: ¹H NMR (500 MHz, CDCl₃): δ 6.00(d, J=4.0 Hz, 1H), 4.90 (dd, J=50.0, 2.4 Hz, 1H), 4.71 (dd, J=11.2, 3.6Hz, 1H), 4.05 (ddd, J=30.4, 8.0, 2.4 Hz, 1H), 3.85 (m, 1H), 2.17 (d,J=1.6 Hz, 1H), 1.61-1.56 (m, 1H), 1.49 (s, 3H), 1.33 (s, 3H), 1.06 (t,J=7.6 Hz, 3H).

Step-6:(S)-1-((3aR,5R,6S,6aS)-6-Fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propylacetate (36S)

To a stirred solution of(S)-1-((3aR,5R,6S,6aS)-6-fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propan-1-ol(35S) (400 mg, 1.80 mmol), TEA (0.51 mL, 3.61 mmol) and DMAP (44 mg,0.36 mmol) in anhydrous CH₂Cl₂ (10 mL) was added acetic anhydride (277mg, 2.71 mmol). After being stirred at 25° C. for 10 h, the reaction wasquenched with a saturated aq. NaHCO₃ solution (20 mL). The organic layerwas separated and the aqueous phase was extracted with CH₂Cl₂ (2×50 mL).The combined organic layers were dried over Na₂SO₄, filtered andconcentrated in vacuum. The crude product was purified by columnchromatography on silica gel (100-200 mesh, 20% EtOAc in petroleumether) to afford (400 mg, 84%) of(S)-1-((3aR,5R,6S,6aS)-6-fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propylacetate (36S) as a colorless oil. C₁₂H₉FO₅: ¹H NMR (500 MHz, CDCl₃): δ5.98 (d, J=3.5 Hz, 1H), 5.23 (m, 1H), 4.89 (dd, J=49.8, 2.5 Hz, 1H),4.69 (dd, J=11.5, 4.0 Hz, 1H), 4.19 (ddd, J=29.8, 8.0, 2.5 Hz, 1H), 2.10(s, 3H), 1.74 (m, 1H), 1.63 (m, 1H), 1.50 (s, 3H), 1.32 (s, 3H), 0.96(t, J=4.0 Hz, 3H).

Step-7:(3S,4S,5R)-5-((S)-1-Acetoxypropyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate (37S)

To a solution of(S)-1-((3aR,5R,6S,6aS)-6-fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propylacetate (36S) (400 mg, 1.52 mmol), acetic acid (0.86 mL, 15.2 mmol) andacetic anhydride (0.72 mL, 7.60 mmol) in anhydrous CH₂Cl₂ (10 mL) wasadded concentrated H₂SO₄ (0.010 mL) at 0° C. After being stirred at RTfor 3 h, the reaction was quenched by addition of a saturated aq. NaHCO₃solution (10 mL). The organic layer was separated and the aqueous phasewas extracted with CH₂Cl₂ (2×50 mL). The combined organic layers weredried over Na₂SO₄, filtered and concentrated in vacuum. The crudeproduct was purified by column chromatography on silica gel (100-200mesh, 30% EtOAc in petroleum ether) to afford (200 mg, 42.8%) of(3S,4S,5R)-5-((S)-1-acetoxypropyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate (37S) as a colorless oil. C₁₃H₁₉FO₇: (2.4:1 mixture of α, βanomers by ¹H NMR); ¹H NMR (400 MHz, CDCl₃): δ 6.47 (d, J=4.8 Hz,0.294H), 6.12 (s, 0.706H), 5.37-4.94 (m, 3H), 4.35-4.25 (m, 1H),2.12-2.08 (m, 9H), 1.74-1.57 (m, 2H), 0.96 (t, J=7.2 Hz, 3H).

Step-8:(S)-1-((2R,3S,4S,5R)-5-(2-Acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxy-3-fluorotetrahydrofuran-2-yl)propylacetate (25B)

Using the procedure described in Example 11, Step-9, replacing(3R,5S)-5-(1-acetoxy-2,2,2-trifluoroethyl)tetrahydrofuran-2,3-diyldiacetate (22S) with(3S,4S,5R)-5-((S)-1-acetoxypropyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate (37S),(S)-1-((2R,3S,4S,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxy-3-fluorotetrahydrofuran-2-yl)propylacetate (25B) in 32% yield after reverse phase GRACE purification (0.1%HCO₂H in water and acetonitrile). C₂₁H₂₄FN₅O₈: ES+, m/z 494.2 [M+H]⁺. ¹HNMR (400 MHz, CDCl₃): δ 11.95 (brs, 1H), 9.30 (s, 1H), 5.84 (m, 2H),5.72 (m, 1H), 5.05 (ddd, J=50.5, 3.4, 1.2 Hz, 1H), 4.84 (m, 2H), 4.24(ddd, J=28.7, 8.9, 3.4 Hz, 1H), 2.30 (s, 3H), 2.28 (m, 1H), 2.14 (s,3H), 2.13 (s, 3H), 1.78 (m, 1H), 1.65 (m, 1H), 0.98 (t, J=7.4, 3H).

Step-9:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 13

Using the procedure described in Example 11, Step-11,2-amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 13 was prepared in 31% yield as a white solid. C₁₅H₁₈FN₅O₅:ES+, m/z 368.3 [M+H]⁺. ¹H NMR (500 MHz, DMSO-d₆): δ 11.16 (brs, 1H),6.65 (brs, 2H), 5.95 (bs, 1H), 5.36 (m, 1H), 5.33 (m, 1H), 4.97 (ddd,1H, J=53.3, 4.5, 2.5 Hz, 1H), 4.84 (d, J=6.5 Hz, 1H), 4.61 (d, J=2.5 Hz,2H), 3.80 (ddd, J=23.5, 6.8, 4.8 Hz, 1H), 3.54 (m, 1H), 3.25 (t, J=2.5Hz, 1H), 1.49 (m, 1H), 1.34 (m, 1H), 0.91 (t, J=7.3 Hz, 3H).

Example 12:2-Amino-9-((2R,3R,5S)-5-((S)-1,2-dihydroxyethyl)-3-hydroxytetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 14

Compound 14 was prepared according to the following multi-stepprocedure.

Step-1:(R)-2-(Benzyloxy)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethan-1-ol(38S)

To a suspension of NaH (60% mineral oil dispersion; 3.4 g, 86.2 mmol) in1,2-dimethoxyethane (40 mL) was added benzyl alcohol (31.2 mL) at 0° C.This was followed by addition of a solution of(3aR,5S,6aR)-2,2-dimethyl-5-((R)-oxiran-2-yl)tetrahydrofuro[2,3-d][1,3]dioxole(9S) (8 g, 43.0 mmol) in 1,2-dimethoxyethane (40 mL) under N₂ atmospherewas at 0° C. The reaction mixture was stirred at 60° C. for 4 h and thenquenched with a saturated NH₄Cl solution (100 mL) and extracted withCHCl₃ (2×300 mL). The combined organic layer was washed with water (100mL) dried over Na₂SO₄, filtered and concentrated in vacuum. The crudemixture was purified by column chromatography on silica gel (100-200mesh, 60% EtOAc in petroleum ether) to afford 10.0 g (79%) of(R)-2-(benzyloxy)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethan-1-ol(38S) as a colourless liquid. C₁₆H₂₂O₅: ¹H NMR (400 MHz, CDCl₃): δ 7.32(m, 5H), 5.80 (d, J 3.6 Hz, 1H), 4.74 (t, J 4.0 Hz, 1H), 4.56 (q,J_(a,b)=12.2 Hz, 2H), 4.23 (dt, J=10.8, 5.0 Hz, 1H), 4.00 (m, 1H), 3.60(dd, J=9.6, 3.6 Hz, 1H), 3.48 (dd, J=10.0, 6.8 Hz, 1H), 2.37 (d, J 3.6Hz, 1H), 2.07 (dd, J=13.4, 4.8 Hz, 1H), 1.85 (m, 1H), 1.57 (s, 3H), 1.27(s, 3H).

Step-2:(S)-2-(Benzyloxy)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethyl4-nitrobenzoate (39S)

To a stirred solution of(R)-2-(benzyloxy)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethan-1-ol(38S) (10.0 g, 32.4 mmol), triphenylphosphine (10.2 g, 38.9 mmol),4-nitrobenzoic acid (5.9 g, 35.7 mmol) in THF (100 mL) was addeddiethylazodicarboxylate (6.1 mL, 38.9 mmol) dropwise at 0° C. under N₂atm. The reaction mixture was stirred at 18° C. for 10 h. Then theresultant mixture was quenched by addition of a saturated NaHCO₃solution (100 mL) and extracted with EtOAc (2×300 mL). The organiclayers were combined, dried over anhydrous Na₂SO₄, filtered andconcentrated in vacuum. The residue was purified by columnchromatography on silica gel (100-200 mesh, 30% EtOAc in petroleumether) to afford 11.5 g (76%) of(S)-2-(benzyloxy)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethyl4-nitrobenzoate (39S) as a light yellow liquid. C₂₃H₂₅NO₈: ¹H NMR (400MHz, CDCl₃): δ 8.26 (m, 4H), 7.28 (m, 5H), 5.82 (d, J=3.6 Hz, 1H), 5.40(m, 1H), 4.72 (t, J=4.2 Hz, 1H), 4.61-4.52 (m, 3H), 3.77 (d, J=5.2 Hz,2H), 2.12 (dd, J=13.2, 4.4 Hz, 1H), 1.69-1.66 (m, 1H), 1.53 (s, 3H),1.32 (s, 3H).

Step-3:(S)-2-(Benzyloxy)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethan-1-ol(40S)

To a stirred solution of(S)-2-(benzyloxy)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethyl4-nitrobenzoate (39S) (11.5 g, 25.9 mmol) in methanol (100 mL) was addedK₂CO₃ (4.1 g, 51.9 mmol). After being stirred at room temperature for 30minutes, the resultant reaction mixture was filtered and the filtratewas concentrated in vacuum. The crude was purified by columnchromatography on silica gel (100-200 mesh, 30% EtOAc in petroleumether) affording 7.0 g (92%)(S)-2-(benzyloxy)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethan-1-ol(40S). C₁₆H₂₂O₅: ¹H NMR (500 MHz, CDCl₃): δ 7.33 (m, 5H), 5.81 (d, J=3.5Hz, 1H), 4.73 (t, J=4.3 Hz, 1H), 4.57 (s, 2H), 4.29 (dt, J=10.5, 4.3 Hz,1H), 3.77 (m, 1H), 3.57 (m, 2H), 2.37 (d, J=5.0 Hz, 1H), 2.02 (dd,J=13.5, 4.5 Hz, 1H), 1.90 (dddd, J=15.5, 9.8, 5.0, 2.5 Hz, 1H), 1.51 (s,3H), 1.32 (s, 3H).

Step-4:(S)-1-((3aR,5S,6aR)-2,2-Dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethane-1,2-diol(41S)

To a stirred solution of(S)-2-(benzyloxy)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethan-1-ol(40S). (5.5 g, 18.7 mmol) in methanol (50 mL) was added 10% Pd/C (2.5 g,50 mol %). The reaction mixture was stirred in a Parr shaker at rt underH₂ at 70 psi for 16 h. Then the reaction mixture was filtered through acelite pad. The celite pad was washed with additional methanol and thefiltrate was concentrated under vacuum. The crude mixture was purifiedby column chromatography on silica gel (100-200 mesh, 10% MeOH inCH₂Cl₂) to afford 3.0 g (78%) of(S)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethylacetate (41S) as a colorless oil. C₉H₁₆O₅: ¹H NMR (400 MHz, CDCl₃): δ5.82 (d, J=3.6 Hz, 1H), 4.75 (t, J=4.2 Hz, 1H), 4.29 (dt, J=10.4, 4.2Hz, 1H), 3.74 (d, J=5.2 Hz, 2H), 3.64 (brs, 1H), 2.50 (s, 1H), 2.27 (s,1H), 2.06 (dd, J=13.4, 4.6 Hz, 1H), 1.93 (dddd, J=15.4, 9.7, 4.6, 2.8Hz, 1H), 1.52 (s, 3H), 1.32 (m, 3H).

Step-5:(S)-1-((3aR,5S,6aR)-2,2-Dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethane-1,2-diyldiacetate (42S)

To a stirred solution of(S)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethylacetate (41S) (2.0 g, 9.8 mmol), TEA (5.4 mL, 39.2 mmol), DMAP (239.2mg, 1.9 mmol) in anhydrous CH₂Cl₂ (20 mL) cooled to 0° C. was addedacetic anhydride (2.9 mL, 29.4 mmol). The reaction mixture was stirredat 25° C. for 16 h and quenched with saturated aq. NaHCO₃ solution (30mL). The organic layer was separated and the aqueous phase was extractedwith CH₂Cl₂ (2×100 mL). The combined organic layers were dried overNa₂SO₄, filtered and concentrated in vacuum. The crude was purified bycolumn chromatography on silica gel (100-200 mesh, 20% EtOAc inpetroleum ether) to afford 2.0 g (71%) of(S)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethane-1,2-diyldiacetate(42S) as a colourless oil. C₁₃H₂₀O₇: ¹H NMR (500 MHz, CDCl₃): δ 5.81 (d,J=3.5 Hz, 1H), 5.18 (dt, J=8.0, 3.8 Hz, 1H), 4.73 (t, J=4.3 Hz, 1H),4.38 (m, 2H), 4.15 (dd, J=12.0, 7.5 Hz, 1H), 2.12 (s, 3H), 2.08 (m, 1H),2.05 (s, 3H), 1.65 (m, 1H), 1.52 (s, 3H), 1.34 (s, 3H).

Step-6: (2S,3R,5S)-5-((S)-1,2-diacetoxyethyl)tetrahydrofuran-2,3-diyldiacetate (43S)

To a solution of(S)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethane-1,2-diyldiacetate(42S) (1.3 g, 4.5 mmol), acetic acid (2.58 mL, 45.1 mmol) and aceticanhydride (2.2 mL, 22.5 mmol) in anhydrous CH₂Cl₂ (20 mL) was addedconcentrated H₂SO₄ (0.04 mL) at 0° C. After being stirred at 22° C. for4 hours, the reaction was quenched by addition of a saturated aq. NaHCO₃solution (100 mL). The organic layer was separated and the aqueous phasewas extracted with CH₂Cl₂ (2×100 mL). The combined organic layers weredried over Na₂SO₄, filtered and concentrated in vacuum. The cruderesidue was purified by column chromatography on silica gel (100-200mesh, 30% EtOAc in petroleum ether) to afford 1.0 g (67%) of(2S,3R,5S)-5-((S)-1,2-diacetoxyethyl)tetrahydrofuran-2,3-diyl diacetate(43S) as a colorless oil. C₁₄H₂₀O₉: ¹H NMR (500 MHz, CDCl₃): δ 6.12 (s,1H), 5.19 (d, J=3.5 Hz, 1H), 5.13 (m, 1H), 4.50 (m, 1H), 4.32 (dd,J=12.0, 4.0 Hz, 1H), 4.10 (dd, J=12.0, 6.5 Hz, 1H), 2.10-2.06 (m, 14H).

Step-7:(S)-1-((2S,4R,5R)-5-(2-Acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)ethane-1,2-diyldiacetate (26)

N-(6,8-dioxo-7-(prop-2-yn-1-yl)-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide(6) (300 mg, 1.2 mmol),(2S,3R,5S)-5-((S)-1,2-diacetoxyethyl)tetrahydrofuran-2,3-diyl diacetate(43S) (483.8 mg, 1.4 mmol), BSA (0.92 mL, 3.6 mmol) were dissolved in1,2-dichloroethane (20 mL) and the resulting reaction mixture wasstirred at 80° C. for 30 min under argon. The reaction mixture wasallowed to warm to RT and 1,2-dichloro ethane was removed under vacuum.The residue was taken up in MeCN (20 mL), followed by addition of TMSOTf(0.33 mL, 1.8 mmol). The stirred reaction mixture was heated at 80° C.for 16 h., cooled to room temperature and concentrated under vacuum. Theresidue obtained was diluted with aq. NaHCO₃ (50 mL) and extracted withEtOAc (3×50 mL). The combined EtOAc layer was washed with water (30 mL),brine (30 mL), dried over Na₂SO₄, filtered and concentrated under vacuumThe crude product was purified by column chromatography on silica gel(100-200 mesh, 80% EtOAc in petroleum ether) to afford 300 mg (47%) of(S)-1-((2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)ethane-1,2-diyldiacetate (26) as an off-white solid. C₂₂H₂₅N₅O₁₀: ES+, m/z 520.2[M+H]⁺.

Step-8:2-Amino-9-((2R,3R,5S)-5-((S)-1,2-dihydroxyethyl)-3-hydroxytetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 14

To a solution of(S)-1-((2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)ethane-1,2-diyldiacetate (26) (300 mg, 0.57 mmol) in MeOH (10 mL) was added K₂CO₃(119.6 mg, 0.86 mmol) at 0° C. The reaction mixture was stirred at RTfor 16 h followed by removal of methanol under reduced pressure at RT.The residue obtained was purified by Prep HPLC Column: X-SELECT-C18(150*19), 5 u Mobile phase: 10 mM NH₄HCO₃ in H₂O:MeCN GRADIENT: (T % B):—0/2, 3/2, 8/20, 10/40, 10/0.1/98, 12/98, 13.1/2, 16/2; Flow Rate: 20mL/min. The pure fractions were lyophilized to afford 35 mg (17%) of2-amino-9-((2R,3R,5S)-5-((S)-1,2-dihydroxyethyl)-3-hydroxytetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 14 as an off white solid. C₁₄H₁₇N₅O₆: ES+, m/z 352.2 [M+H]⁺. ¹HNMR (400 MHz, DMSO-d₆): δ 11.76 (brs, 1H), 6.71 (s, 2H), 5.50 (d, J 3.6Hz 1H), 5.38 (d, J=4.4 Hz, 1H), 4.90 (bs, 1H), 4.75 (m, 1H), 4.60 (s,2H), 4.47 (m, 1H), 4.17 (m, 1H), 3.37-3.32 (m, 3H), 3.20 (t, J 2.2 Hz,1H), 2.40 (m, 1H), 1.85 (m, 1H).

Example13:2-Amino-9-((2R,3R,5S)-5-((S)-2-amino-1-hydroxyethyl)-3-hydroxytetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 15

Compound 15 was prepared according to the following multi-stepprocedure.

Step-1:(R)-2-Azido-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethan-1-ol(44S)

To a solution of(3aR,5S,6aR)-2,2-dimethyl-5-((R)-oxiran-2-yl)tetrahydrofuro[2,3-d][1,3]dioxole(9S) (4.0 g, 21.71 mmol) in DMF (40 mL) was added TMSN₃ (8 mL, 2 vol)and methanol (8 mL, 2 vol) at 60° C. The reaction was monitored by TLC.After stirring at 60° C. for 48 h. the reaction mixture was poured into400 mL of ice-water and extracted with EtOAc (2×300 mL). The solutionwas further washed with a sat. brine solution (2×100 mL) and the organiclayer was separated, dried over anhydrous Na₂SO₄, filtered andconcentrated to afford crude(R)-2-azido-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethan-1-ol(44S) (˜4.0 g crude, 80%) as a liquid. C₉H₁₅N₃O₄: The crude product wasdirectly used in next step reaction. ¹H NMR (400 MHz, CDCl₃): δ 5.80 (d,J=3.2 Hz, 1H), 4.77 (t, J=4.0 Hz, 1H), 4.19 (dt, J 10.3, 4.6 Hz, 1H),3.99 (m, 1H), 3.37 (m, 2H), 2.30 (m, 1H), 2.08 (dd, J=13.2, 4.6 Hz, 1H),1.86 (ddd, J=15.4, 9.7, 4.8 Hz, 1H), 1.55 (s, 3H), 1.33 (s, 3H).

Step-2: (S)-2-Azido-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][,3]dioxol-5-yl)ethyl 4-nitrobenzoate (45S)

To a solution of(R)-2-azido-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethan-1-ol(44S) (4 g, 17.44 mmol) in THF (60 mL) was added 4-nitrobenzoic acid(5.8 g, 34.8 mmol) and triphenylphosphine (9.1 g, 34.89 mmol) and DEAD(5.4 mL, 34.8 mmol) at 0° C. The reaction was stirred at RT andmonitored by TLC. After 16 h the reaction mixture was poured into 200 mLof water and extracted with EtOAc (2×200 mL). The organic layer wasfurther washed with a sat. brine solution (2×60 mL), dried overanhydrous Na₂SO₄, filtered and concentrated to afford the crude product.The crude product was purified by column chromatography on silica gel(100-200 mesh, 30% EtOAc in petroleum ether) to afford(S)-2-azido-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethyl4-nitrobenzoate (45S) (4.0 g, 60%) as a semi solid. C₁₆H₁₈N₄O₇: ES−, m/z377.1 [M−H]⁻. ¹H NMR (400 MHz, CDCl₃): δ 8.33-8.24 (m, 4H), 5.84 (d,J=3.6 Hz, 1H), 5.37 (m, 1H), 4.75 (t, J=4.2 Hz, 1H), 4.51 (dt, J=10.7,4.6 Hz, 1H), 3.67 (d, J=4.8 Hz, 2H), 2.16 (dd, J=13.2, 4.8 Hz, 1H), 1.66(ddd, J=15.6, 9.6, 3.6 Hz 1H), 1.55 (s, 3H), 1.33 (s, 3H).

Step-3:(S)-2-Azido-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethan-1-ol(46S)

To a solution of(S)-2-azido-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethyl4-nitrobenzoate (45S) (4.0 g, 10.572 mmol) in methanol (40 mL, 10 vol),was added K₂CO₃ (2.9 g, 21.1 mmol) at rt. The reaction was monitored byTLC. After stirring at rt for 1 h the reaction mixture was filteredthrough a plug of silica gel, and the filtrate was concentrated undervacuum to afford(S)-2-azido-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethan-1-ol(46S) (2.2 g, 83%) as a liquid that was used without furtherpurification. C₉H₁₅N₃O₄: ¹H NMR (400 MHz, CDCl₃): δ 5.81 (m, 1H), 4.75(t, J=3.8 Hz, 1H), 4.24-4.13 (m, 2H), 3.85 (m, 1H), 3.40 (m, 1H), 2.02(m, 1H), 1.88 (m, 1H), 1.74 (m, 1H), 1.53 (s, 3H), 1.36 (s, 3H).

Step-4:(S)-2-Azido-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethylacetate (47S)

To a stirred solution of(S)-2-azido-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethan-1-ol(46S) (2.2 g, 9.59 mmol), TEA (2.67 mL, 19.19 mmol), DMAP (0.23 g, 1.91mmol) in anhydrous dichloromethane (22 mL) was added acetic anhydride(1.37 mL, 14.39 mmol). After being stirred at 25° C. for 10 h, thereaction was quenched by the saturated aq. NaHCO₃ solution (50 mL). Theorganic layer was separated and the aqueous phase was extracted with DCM(2×50 mL). The combined organic layers were dried over Na₂SO₄ andconcentrated in vacuum. The crude was purified by column chromatographyon silica gel (100-200 mesh, eluting with 20% EtOAc in Petroleum ether)to afford(S)-2-azido-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethylacetate (47S) (2 g, 86%) as a colourless oil. C₁₁H₁₇N₃O₅: ¹H NMR (500MHz, CDCl3): δ 5.81 (d, J=4.0 Hz, 1H), 5.09 (q, J=2.3 Hz, 1H), 4.74 (t,J=4.5 Hz, 1H), 4.36 (dt, J=6.0, 4.5 Hz, 1H), 4.27 (m, 1H), 3.50 (dd,J=6.5, 4.0 Hz, 2H), 2.15 (s, 3H), 1.64-1.58 (m, 1H), 1.57 (s, 3H), 1.32(s, 3H).

Step-5:(2S,3R,5S)-5-((S)-1-Acetoxy-2-azidoethyl)tetrahydrofuran-2,3-diyldiacetate (48S)

To a solution of(S)-2-azido-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethylacetate (47S) (2.0 g, 7.3 mmol), acetic acid (4.21 mL, 73.72 mmol) andacetic anhydride (3.48 mL, 36.86 mmol) in anhydrous CH₂Cl₂ (40 mL) wasadded concentrated H₂SO₄ (0.1 mL) at 0° C. After being stirred at 25° C.for 3 h, the reaction was quenched by addition of saturated aq. NaHCO₃solution (100 mL). The organic layer was separated and the aqueous phasewas extracted with CH₂Cl₂ (2×100 mL). The combined organic layers weredried over Na₂SO₄, filtered and concentrated in vacuum. The crude oilwas purified by column chromatography on silica gel (100-200 mesh, 30%EtOAc in petroleum ether) to afford(2S,3R,5S)-5-((S)-1-acetoxy-2-azidoethyl)tetrahydrofuran-2,3-diyldiacetate (48S) (1.1 g, 45%) as a colourless oil. C₁₂H₁₇N₃O₇: ¹H NMR(500 MHz, CDCl₃): δ 6.12 (s, 1H), 5.18 (d, J=5.0 Hz, 1H), 5.04 (m, 1H),4.52 (m, 1H), 3.46 (m, 2H), 2.15 (m, 2H), 2.09-2.07 (s, 9H).

Step-6:(S)-1-((2S,4R,5R)-5-(2-Acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2-azidoethylacetate (27)

To a suspension ofN-(6,8-dioxo-7-(prop-2-yn-1-yl)-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide(6) (700 mg, 2.83 mmol) and(2S,3R,5S)-5-((S)-1-acetoxy-2-azidoethyl)tetrahydrofuran-2,3-diyldiacetate (48S) (1.07 g, 3.40 mmol) in acetonitrile (30 mL) was addedBSA (2.15 mL, 8.49 mmol). The reaction mixture was stirred at 70° C. for1 h under argon to form a clear solution. TMSOTf (0.78 mL, 4.24 mmol)was added at 0° C. After being heated with stirring at 70° C. for 16 h,the reaction was quenched with water (60 mL), extracted with EA (2×70mL). The combined organic layers were dried over Na₂SO₄, filtered andconcentrated in vacuum. The residue was purified by column on silica gel(80% EtOAc in petroleum ether) to afford(S)-1-((2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2-azidoethylacetate (27) (0.50 g, 40%) as an off-white solid. C₂₀H₂₂N₈O₈: ES+, m/z503.3 [M+H]⁺.

Step-7:2-Amino-9-((2R,3R,5S)-5-((S)-2-azido-1-hydroxyethyl)-3-hydroxytetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione(28)

To a solution of(S)-1-((2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2-azidoethylacetate (27) (500 mg, 0.99 mmol) in methanol (30 mL), was added K₂CO₃(138 mg, 0.99 mmol) at rt. The reaction mixture was stirred at roomtemperature and monitored by LC/MS. After 16 h the starting material wasconsumed. The reaction mixture was concentrated under vacuum to affordcrude2-amino-9-((2R,3R,5S)-5-((S)-2-azido-1-hydroxyethyl)-3-hydroxytetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione(28) (370 mg, 55%) as a crude solid material that was used in the nextstep without purification. C₁₄H₁₆N₈O₅: ES+, m/z 377.3 [M+H]⁺.

Step-8:2-2-Amino-9-((2R,3R,5S)-5-((S)-2-amino-1-hydroxyethyl)-3-hydroxytetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 15

To a stirred solution of2-amino-9-((2R,3R,5S)-5-((S)-2-azido-1-hydroxyethyl)-3-hydroxytetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione(28) (350 mg, 0.930 mmol) in THE at rt (7 mL, 20 vol), was addedtriphenyphosphine (487 mg, 1.86 mmol) and water (3.5 mL, 1 vol). Themixture was stirred at 60° C. The reaction was monitored by LCMS andafter 16 h the starting material was consumed. The reaction mixture wasconcentrated under vacuum to afford a thick solid that was subjected toGRACE reverse phase chromatography (10 mmol NH₄HCO₃:MeCN) to afford2-amino-9-((2R,3R,5S)-5-((S)-2-amino-1-hydroxyethyl)-3-hydroxytetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione(Compound 15) (30 mg, 20%) as an off-white solid. C₁₄H₁₈N₆O₅: ¹H NMR(500 MHz, DMSO-d₆): δ 6.66 (bs, 2H), 5.50 (d, J=3.0 Hz, 1H), 5.38 (d,J=4.0 Hz, 1H), 4.95 (bs, 1H), 4.74 (d, J=3.0 Hz, 1H), 4.64 (s, 2H), 4.09(q, J=6.7 Hz, 1H), 3.31 (s, 1H), 3.20 (t, J=2.3 Hz, 1H), 2.59-2.54 (m,1H), 2.46-2.37 (m, 2H), 1.91-1.71 (m, 1H). ES+, m/z 351.2 [M+H]⁺.

Example 14:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxy-2-(methylamino)ethyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 16

Compound 16 was prepared according to the following multi-stepprocedure.

Step-1:(R)-2-((tert-Butyldimethylsilyl)oxy)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethan-1-ol(49S)

To a solution of(R)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethane-1,2-diol(3S) (10.0 g, 49.01 mmol) in DMF (100 mL), was added TBDMS-Cl (7.35 g,49.01 mmol) and imidazole (4.29 g, 63.21 mmol) at 0° C. The reactionmixture was stirred at 25° C. and monitored by TLC. After 8 h thereaction mixture was poured into 600 mL of ice-water and extracted withEtOAc (2×500 mL). It was further washed with brine solution (2×200 mL)and all organic layers were collected, dried over anhydrous Na₂SO₄,filtered and concentrated. The crude product was filtered through a padof silica to afford(R)-2-((tert-butyldimethylsilyl)oxy)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethan-1-ol(49S) (10.0 g, 65%) as a semi-solid and used as is. C₁₅H₃₀O₅Si: ¹H NMR(400 MHz, CDCl₃): δ 5.80 (d, J=3.6 Hz, 1H), 4.74 (t, J=4.0 Hz, 1H), 4.20(m, 1H), 3.75 (m, 2H), 3.71-3.65 (m, 1H), 2.15 (m, 1H), 1.83 (m, 1H),1.56-1.53 (m, 1H), 1.51 (s, 3H), 1.36 (s, 3H), 0.91 (s, 9H), 0.08 (s,6H).

Step-2:(R)-2-((tert-Butyldimethylsilyl)oxy)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethylmethanesulfonate (50S)

To a solution of(R)-2-((tert-butyldimethylsilyl)oxy)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethan-1-ol)(49S) (10.0 g, 31.446 mmol) in CH₂Cl₂ (100 mL) cooled to 0° C. was addedTEA (14.24 mL, 110.06 mmol) and mesyl chloride (3.63 mL, 47.16 mmol).The stirred reaction mixture was warmed to rt and monitored by TLC.After 16 hrs the reaction mixture was poured into 500 mL of water andextracted with CH₂Cl₂ (2×500 mL). The mixture was washed with brinesolution (2×200 mL), the organic layers were collected, dried overanhydrous Na₂SO₄, filtered and concentrated to afford crude(R)-2-((tert-butyldimethylsilyl)oxy)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethylmethanesulfonate (50S) (11 g, 80%) as a liquid and used as is.C₁₆H₃₂O₇SSi: ¹H NMR (500 MHz, CDCl3): δ 5.78 (d, J=3.5 Hz, 1H), 4.76 (d,J=4.0 Hz, 1H), 4.42 (m, 1H), 3.83 (d, J=5.0 Hz, 2H), 3.07 (s, 3H), 2.19(m, 1H), 1.93 (m, 1H), 1.51 (s, 3H), 1.45-1.33 (m, 1H), 1.32 (s, 3H),0.90 (s, 9H), 0.08 (s, 6H).

Step-3:(3aR,5S,6aR)-2,2-Dimethyl-5-((S)-oxiran-2-yl)tetrahydrofuro[2,3-d][1,3]dioxole(51S)

To a solution of(R)-2-((tert-butyldimethylsilyl)oxy)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethylmethanesulfonate (50S) (11 g, 27.7 mmol) in THE (55 mL) was added 1MTBAF in THE (83.3 mL, 83.3 mmol) at 0° C. The reaction mixture wasconcentrated to afford crude that was subjected to column chromatographyon silica gel (100-200 mesh, eluting with 25% EtOAc in petroleum ether)to afford(3aR,5S,6aR)-2,2-dimethyl-5-((S)-oxiran-2-yl)tetrahydrofuro[2,3-d][1,3]dioxole[20720-51-8] (51S) (3.0 g, 57%) as a liquid. C₉H₁₄O₄: ¹H NMR (400 MHz,CDCl₃): δ 5.81 (d, J=3.6 Hz, 1H), 4.75 (t, J=4.2 Hz, 1H), 4.18 (dt,J=10.8, 4.6 Hz, 1H), 3.04 (q, J=3.6 Hz, 1H), 2.81 (d, J=5.6 Hz, 2H),2.16 (dd, J=13.4, 4.6 Hz, 1H), 1.85 (ddd, J=15.4, 9.8, 3.6 Hz, 1H), 1.50(s, 3H), 1.36 (s, 3H).

Step-4:(S)-1-((3aR,5S,6aR)-2,2-Dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)-2-(methylamino)ethan-1-ol(52S)

To a stirred solution of(3aR,5S,6aR)-2,2-dimethyl-5-((S)-oxiran-2-yl)tetrahydrofuro[2,3-d][1,3]dioxole(51S) (3.0 g, 15.9 mmol) was added methyl amine in THE (2M, 45 mL, 15vol), in anhydrous THE (30 mL). The reaction mixture was stirred at 75°C. in a sealed tube. After 24 hrs, TLC indicated consumption of (51S).The mixture was concentrated in vacuum to afford crude(S)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)-2-(methylamino)ethan-1-ol)(52S) (3.1 g, 86%) as a semi solid that was used in the next stepwithout purification. C₁₀H₁₉NO₄: ¹H NMR (500 MHz, CDCl₃): δ 5.81 (d,J=3.5 Hz, 1H), 4.75 (m, 1H), 4.08-4.21 (m, 1H), 3.67-3.81 (m, 1H),2.79-2.91 (m, 2H), 2.53 (s, 3H), 2.27-2.44 (b, 2H), 1.97-2.04 (m, 2H),1.51 (s, 3H), 1.32 (s, 3H).

Step-5:(S)-1-((3aR,5S,6aR)-2,2-Dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)-2-(2,2,2-trifluoro-N-methylacetamido)ethyl2,2,2-trifluoroacetate (53S)

To a stirred solution of(S)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)-2-(methylamino)ethan-1-ol)(52S) (3.1 g, 14.28 mmol), TEA (7.4 mL, 57.142 mmol), DMAP (0.234 g,2.85 mmol) in anhydrous CH₂Cl₂ (31 mL) was added trifluro aceticanhydride (3.99 mL, 28.57 mmol). The reaction mixture was heated at 25°C. for 16 h, and then quenched with a saturated aq. NaHCO₃ solution (60mL). Then the organic layer was separated and the aqueous phase wasextracted with CH₂Cl₂ (2×60 mL). The combined organic layers were driedover anhydrous Na₂SO₄, filtered and concentrated in vacuum. The crudeproduct was purified by column chromatography on silica gel (100-200mesh, 20% EtOAc in petroleum ether) to afford(S)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)-2-(2,2,2-trifluoro-N-methylacetamido)ethyl2,2,2-trifluoroacetate (53S) (2 g, 86%) as a viscous liquid.C₁₄H₁₇F₆NO₆: (¹H NMR indicates NEt₃ salt impurities)¹H NMR (400 MHz,CDCl₃): δ 5.82 (d, J=3.6 Hz, 1H), 4.76 (t, J=4.2 Hz, 1H), 4.18 (m, 1H),3.88 (m, 1H), 3.62 (dd, J=13.8, 3.6 Hz, 1H), 3.49 (dd, J=9.0, 2.4 Hz,1H), 3.26 (m, 3H), 2.09 (dd, J=13.4, 4.6 Hz, 1H), 1.88-1.95 (m, 1H),1.51 (s, 3H), 1.30 (s, 3H).

Step-6:(2S,3R,5S)-5-((S)-1-Acetoxy-2-(2,2,2-trifluoro-N-methylacetamido)ethyl)tetrahydrofuran-2,3-diyldiacetate (54S)

To a solution of(S)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)-2-(2,2,2-trifluoro-N-methylacetamido)ethyl2,2,2-trifluoroacetate (53S) (2.0 g, 4.8 mmol), acetic acid (1.78 mL,29.33 mmol) and acetic anhydride (3.01 mL, 29.34 mmol) in anhydrousCH₂Cl₂ (40 mL) was added concentrated H₂SO₄ (0.1 mL) at 0° C. Theresulting reaction mixture was stirred at 22° C. for 3 hrs and wasquenched by addition of saturated aq. NaHCO₃ solution (200 mL). Theorganic layer was separated and the aqueous phase was extracted withCH₂Cl₂ (2×200 mL). The combined organic layers were dried over Na₂SO₄,filtered and concentrated in vacuum. The crude was purified by columnchromatography on silica gel (100-200 mesh, 15% EtOAc in petroleumether) to afford(2S,3R,5S)-5-((S)-1-acetoxy-2-(2,2,2-trifluoro-N-methylacetamido)ethyl)tetrahydrofuran-2,3-diyldiacetate (1.1 g, 47%) as a viscous liquid that was used without furtherpurification. C₁₅H₂₀F₃NO₈: (¹H NMR indicates NEt₃ salt impurities)¹H NMR(400 MHz, CDCl₃): δ 6.11 (s, 1H), 5.32 (m, 1H), 5.25 (m, 1H), 5.19 (d,J=4.4 Hz, 1H), 4.41 (m, 1H), 3.68 (m, 1H), 3.60 (m, 1H), 3.18 (s, 3H),3.04 (s, 1H), 2.09 (m, 9H).

Step-7:(S)-1-((2S,4R,5R)-5-(2-Acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2-(2,2,2-trifluoro-N-methylacetamido)ethylacetate (29)

To a mixture ofN-(6,8-dioxo-7-(prop-2-yn-1-yl)-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide(6) (400 mg, 1.619 mmol) and(2S,3R,5S)-5-((S)-1-acetoxy-2-(2,2,2-trifluoro-N-methylacetamido)ethyl)tetrahydrofuran-2,3-diyldiacetate (54S) (840 mg, 2.10 mmol) in 1,2-dichloroethane (40 mL) wasadded BSA (1.23 mL, 4.8 mmol). The reaction mixture was stirred at 80°C. for 30 min under argon at which time the resulting solution wasallowed to cool to RT and 1,2-dichloroethane was removed under vacuum.The residue was taken up in MeCN (40 mL) followed by addition of TMSOTf(0.449 mL, 2.4 mmol). The reaction mixture was heated at 80° C. for 16h, cooled to room temperature and concentrated under vacuum. The residuewas diluted with sat. aq. NaHCO₃ (60 mL) and extracted with EtOAc (3×80mL). The combined EtOAc layers were washed with water (50 mL), brine (40mL), dried over anhydrous Na₂SO₄, filtered and concentrated undervacuum. The crude compound was purified by flash column chromatographyon silica gel (100-200 mesh, 80% EtOAc in Pet ether) to afford(S)-1-((2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2-(2,2,2-trifluoro-N-methylacetamido)ethylacetate (29) (260 mg, 28%) as an off-white solid. C₂₃H₂₅F₃N₆O₉: ¹H NMR(400 MHz, DMSO-d₆): δ 11.20-11.80 (b, 1H), 5.71 (s, 1H), 5.66 (d, J=6.0Hz, 1H), 5.26-5.37 (m, 1H), 4.68 (s, 2H), 4.32 (m, 1H), 3.78 (m, 1H),3.55 (m, 1H), 3.08 (s, 3H), 2.89 (m, 2H), 2.81 (m, 1H), 2.17 (s, 3H),2.07 (s, 3H), 2.02 (m, 1H), 1.93 (s, 3H). ES+, m/z 586.9 [M+H]⁺.

Step-8:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxy-2-(methylamino)ethyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dioneCompound 16

To a solution of(S)-1-((2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2-(2,2,2-trifluoro-N-methylacetamido)ethylacetate (29) (260 mg, 0.443 mmol) in methanol (10 mL) was added K₂CO₃(91.8 mg, 0.665 mmol) at rt. The resultant reaction mixture was stirredat room temperature and monitored by LC/MS. After 16 hrs the startingmaterial was consumed. The reaction mixture was concentrated undervacuum, to afford a thick slurry that was subjected to GRACE reversephase chromatography (10 mM aq. (NH₄)HCO₃:MeCN) to afford2-amino-9-(2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxy-2-(methylamino)ethyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione(Compound 16) (71 mg, 44%) as an off-white solid. C₁₅H₂₀N₆O₅: ¹H NMR(400 MHz, DMSO-d₆; D20): δ 5.53 (d, J=3.6 Hz, 1H), 4.74 (m, 1H), 4.62(s, 2H), 4.12 (m, 1H), 3.58 (m, 1H), 3.16 (t, J=2.4 Hz, 1H), 2.36-2.48(m, 3H), 2.96 (s, 3H), 1.86 (m, 1H). ES+, m/z 365.3 [M+H]⁺.

Example 15:2-Amino-7-(cyclopropylmethyl)-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 17

Using the methods described in Examples 3 and 11, Compound 17 wasprepared according to the following procedure from (12) and (37S).

Step-1:(S)-1-((2R,3S,4S,5R)-5-(2-Acetamido-7-(cyclopropylmethyl)-6,8-dioxo-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxy-3-fluorotetrahydrofuran-2-yl)propylacetate (30)

N-(7-(Cyclopropylmethyl)-6,8-dioxo-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide(12) (300 mg, 1.1 mmol),(3S,4S,5R)-5-((S)-1-acetoxypropyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate (37S) (523.5 mg, 1.7 mmol) and BSA (0.86 mL, 3.42 mmol) weredissolved in 1,2-dichloroethane (20 mL) and the resulting reactionmixture was stirred at 80° C. for 30 min under argon. The reactionmixture was allowed to cool to RT and 1,2-dichloroethane was removed byvacuum. The residue was dissolved in MeCN (20 mL) followed by additionof TMSOTf (0.31 mL, 1.71 mmol). The reaction mixture was heated at 80°C. for 16 h, cooled to room temperature and concentrated under vacuum.The residue was diluted with sat. aq. NaHCO₃ (60 mL) and extracted withEtOAc (3×60 mL). The combined EtOAc layers were washed with water (30mL), brine (30 mL), dried over anhydrous Na₂SO₄, filtered andconcentrated under vacuum. The crude compound was purified by flashcolumn chromatography (silica gel, 100-200 mesh, 80% EtOAc in pet ether)to afford 230 mg (39%) of(S)-1-((2R,3S,4S,5R)-5-(2-acetamido-7-(cyclopropylmethyl)-6,8-dioxo-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxy-3-fluorotetrahydrofuran-2-yl)propylacetate (30) as a pale yellow solid. C₂₂H₂₈FN₅O₅: ES+, m/z 510.8 [M+H]⁺.

Step-2:2-Amino-7-(cyclopropylmethyl)-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 17

To a solution of(S)-1-((2R,3S,4S,5R)-5-(2-acetamido-7-(cyclopropylmethyl)-6,8-dioxo-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxy-3-fluorotetrahydrofuran-2-yl)propylacetate (30) (230 mg, 0.45 mmol) in methanol (10 mL) was added K₂CO₃(62.3 mg, 0.45 mmol) at rt. The reaction mixture was stirred at roomtemperature for 16 h and concentrated under vacuum to afford a solidmass. The crude product was purified by Prep-HPLC, Column Luna@omega(250*21.2), 5 u Mobile phase: 0.1% HCO₂H in H₂O:MeCN Gradient: (T %B):—0/5, 8/50, 10.5/50, 10.6/98, 12/98, 12.1/5, 15/5 Flow Rate: 17mL/min to afford 16 mg (9%) of2-amino-7-(cyclopropylmethyl)-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7,9-dihydro-1H-purine-6,8-dione(Compound 17) as a white solid. C₁₆H₂₂FN₅O₅: The ¹H NMR spectrumindicated the product to be a formic acid salt; ¹H NMR (400 MHz,DMSO-d₆, D₂O): δ 8.48 (s, 1H), 5.39 (d, J=6.4 Hz, 1H), 5.38-5.29 (m,1H), 5.00 (ddd, J=52.8, 4.8, 2.6 Hz, 1H), 3.85 (dt, J=22.0, 5.7 Hz, 1H),3.67 (d, J 5.6 Hz, 2H), 3.52 (m, 1H), 1.51 (m, 1H), 1.36 (m, 1H), 1.19(m, 1H), 0.91 (t, J 7.2 Hz, 3H), 0.43 (m, 2H), 0.38 (m, 2H). ES+, m/z384.2 [M+H]⁺.

Example 16:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-(2-hydroxypropan-2-yl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 18

Compound 18 was prepared according to the following multi-stepprocedure.

Step-1:1-((3aR,5S,6aR)-2,2-Dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethan-1-one(55S)

To a stirred solution of(R)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethan-1-ol(15S) (7 g, 37.2 mmol) in CH₂Cl₂ (70 mL) at 0° C. under N₂ atm wereadded pyridinium dichromate (16.7 g, 44.6 mmol) followed by the dropwiseaddition of acetic anhydride (7 mL, 1 vol). The reaction mixture wasstirred at rt for 16 h, concentrated under reduced pressure and theresidue was purified by column chromatography on silica gel (100-200mesh, 50% EtOAc in petroleum ether) to afford 5 g (66%) of1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethan-1-one(55S) as a light yellow liquid. C₉H₁₄O₄: ¹H NMR (400 MHz, CDCl₃): δ 5.93(d, J=3.2 Hz, 1H), 4.76 (t, J=4.0 Hz 1H), 4.61 (dd, J=11.2, 5.2 Hz, 1H),2.37 (dd, J=13.4, 5.0 Hz, 1H), 2.24 (s, 3H), 1.77 (m, 1H), 1.52 (s, 3H),1.34 (s, 3H).

Step-2:2-((3aR,5S,6aR)-2,2-Dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propan-2-ol(56S)

To a stirred solution of1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethan-1-one(55S) (5.0 g, 26.8 mmol) in diethyl ether (50 mL) at 0° C. was addedmethyl magnesium bromide (3.0 M) (22.4 mL 67.20 mmol). After thereaction mixture was stirred at room temperature for 3 h it was quenchedwith an aqueous saturated ammonium chloride solution. The organic layerwas separated and the aqueous phase was extracted with EtOAc (2×200 mL).The combined organic layer were dried over Na₂SO₄, filtered andconcentrated under vacuum. The crude oil was purified by columnchromatography on silica gel (100-200 mesh, 50% EtOAc in petroleumether) to afford 2 g (37%) of2-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propan-2-ol(56S). C₁₀H₁₈O₄: ¹H NMR (400 MHz, CDCl₃): δ 5.81 (d, J=2.4 Hz, 1H), 4.72(s, 1H), 4.07 (dd, J=10.4, 4.4 Hz, 1H), 1.99 (dd, J=13.2, 4.4 Hz, 1H),1.95 (m, 1H), 1.85 (m, 1H), 1.53 (s, 3H), 1.33 (s, 3H), 1.31 (s, 3H),1.13 (s, 3H).

Step-3:2-((3aR,5S,6aR)-2,2-Dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propan-2-yl2,2,2-trifluoroacetate (57S)

To a stirred ice cold solution of2-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propan-2-ol(56S) (2.0 g, 9.9 mmol) in anhydrous CH₂Cl₂ (30 mL) was added TEA (4.1mL, 29.70 mmol), DMAP (0.24 g, 1.9 mmol) and trifluoroacetic anhydride(3.4 mL, 24.7 mmol). The reaction mixture was stirred at rt for 16 h andwas then quenched with a saturated aq. NaHCO₃ solution (30 mL). Theorganic layer was separated and the aqueous phase was extracted withCH₂Cl₂ (2×100 mL). The combined organic layers were dried over Na₂SO₄,filtered and concentrated under vacuum. The crude product was purifiedby column chromatography on silica gel (100-200 mesh, 20% EtOAc inpetroleum ether) to afford 1.5 g (51%) of2-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propan-2-yl2,2,2-trifluoroacetate (57S) as a colorless oil. C₁₂H₁₇F₃O₅: ¹H NMR (400MHz, CDCl₃): δ 5.82 (d, J 3.6 Hz, 1H), 4.76 (t, J=4.2 Hz, 1H), 4.26 (dd,J=10.8, 4.8 Hz, 1H), 2.10 (dd, J=13.6, 4.8 Hz, 1H), 1.84 (ddd, J=15.4,9.5, 4.0 Hz, 1H), 1.65 (s, 3H), 1.57 (s, 3H), 1.52 (s, 3H), 1.33 (s,3H).

Step-4:(2S,3R,5S)-5-(2-(2,2,2-Trifluoroacetoxy)propan-2-yl)tetrahydrofuran-2,3-diyldiacetate (58S)

To a solution of2-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propan-2-yl2,2,2-trifluoroacetate (57S) (1.5 g, 5.03 mmol), acetic acid (1.4 mL,25.1 mmol) and acetic anhydride (2.5 mL, 25.1 mmol) in anhydrous CH₂Cl₂(15 mL) was added concentrated H₂SO₄ (0.1 mL) at 0° C. The reactionmixture was stirred at 25° C. for 3 hours and then was quenched byaddition of a saturated aq. NaHCO₃ solution (100 mL). The organic layerwas separated and the aqueous phase was extracted with CH₂Cl₂ (2×100mL). The combined organic layers were dried over anhydrous Na₂SO₄,filtered and concentrated under vacuum. The crude oil was purified bycolumn chromatography on silica gel (100-200 mesh, 30% EtOAc inpetroleum ether) to afford 0.7 g (41%) of(2S,3R,5S)-5-(2-(2,2,2-trifluoroacetoxy)propan-2-yl)tetrahydrofuran-2,3-diyldiacetate (58S). C₁₃H₁₇F₃O₇: ¹H NMR (400 MHz, CDCl₃): δ 6.16 (s, 1H),5.20 (d, J=4.8 Hz, 1H), 4.38 (dd, J=10.4, 6.0 Hz, 1H), 2.25-2.21 (m,2H), 2.10 (s, 3H), 2.07 (s, 3H), 1.65 (s, 3H), 1.57 (s, 3H).

Step-5:2-((2S,4R,5R)-5-(2-Acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)propan-2-yl2,2,2-trifluoroacetate (31)

N-(6,8-dioxo-7-(prop-2-yn-1-yl)-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide(6) (350 mg, 1.4 mmol),(2S,3R,5S)-5-(2-(2,2,2-trifluoroacetoxy)propan-2-yl)tetrahydrofuran-2,3-diyldiacetate (58S) (726.9 mg, 2.12 mmol) and BSA (1.07 mL, 4.25 mmol) weredissolved in 1,2-dichloroethane (15 mL). The resulting reaction mixturewas stirred at 80° C. for 30 min under argon, allowed to cool to roomtemperature and the solvent was removed by vacuum. The residue wasdissolved in MeCN (20 mL) followed by addition of TMSOTf (0.39 mL, 2.1mmol). The reaction mixture was heated at 70° C. for 16 h, cooled toroom temperature and concentrated under vacuum. The residue was dilutedwith sat. aq. NaHCO₃ (50 mL) and extracted with EtOAc (3×50 mL). Thecombined EtOAc layer were washed with water (30 mL), brine (20 mL),dried over Na₂SO₄, filtered and concentrated under vacuum. The crudecompound was purified by GRACE chromatography (80% EtOAc in pet. ether)to afford 270 mg (49%) of2-((2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)propan-2-yl2,2,2-trifluoroacetate (31) as an off-white solid. C₂₁H₂₂F₃N₅O₈: ES+,m/z 529.9 [M+H]⁺.

Step-6:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-(2-hydroxypropan-2-yl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 18

To a solution of2-((2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)propan-2-yl2,2,2-trifluoroacetate (31) (270 mg, 0.51 mmol) in MeOH (10 mL) wasadded K₂CO₃ (105.6 mg, 0.76 mmol) at 0° C. The reaction mixture wasstirred at RT for 16 h and neutralized with acetic acid at 0° C.Methanol was removed under reduced pressure at RT and the residueobtained was purified by Prep-HPLC. Column: X-SELECT-C18 (250*19), 5 uMobile phase: 0.1% HCO₂H in H₂O:MeOH gradient: (T % B):—0/20, 8/,50,10.5/50, 10.6/98, 13/98, 13.1/20, 16/20 Flow Rate: 18 mL/min. The purefractions were subjected to lyophilization having 45 mg (25%) of2-amino-9-((2R,3R,5S)-3-hydroxy-5-(2-hydroxypropan-2-yl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione(Compound 18) as an off white solid. C₁₅H₁₉N₅O₅: ¹H NMR (500 MHz,DMSO-d₆): δ 10.80 (brs, 1H), 6.53 (brs, 2H), 6.51 (brs, 1H), 5.49 (d,J=3.5 Hz, 1H), 5.37 (d, J=4.5 Hz, 1H), 4.76 (m, 1H), 4.59 (d, J=1.5 Hz,2H), 4.38 (s, 1H), 3.91 (t, J=7.3 Hz, 1H), 3.23 (s, 1H), 2.46-2.41 (m,1H), 1.75 (m, 1H), 1.03 (d, J=6.0 Hz, 6H). ES+, m/z 350.0 [M+H]⁺.

Example 17:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-(2-hydroxypropan-2-yl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 19

Compound 19 was prepared according to the following multi-stepprocedure.

Step-1:1-((3aR,5R,6S,6aS)-6-Fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethan-1-ol(59S)

To a solution of(3aR,5R,6S,6aS)-6-fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxole-5-carbaldehyde(27S) (1 g, 5.26 mmol) in THE (20 mL) was added methyl magnesium bromide(1M in THF, 15.8 mL, 15.78 mmol) at −20° C. under argon. The reactionmixture was stirred at room temperature for 6 h and then it was quenchedwith a saturated aq. NH₄Cl solution and extracted with EtOAc (3×100 mL).The combined organic layers were dried over anh. Na₂SO₄, filtered andconcentrated in vacuum to afford the crude product that was purified bycolumn chromatography on silica gel (1:4 EtOAc in Pet-ether).1-((3aR,5R,6S,6aS)-6-fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethan-1-ol(59S) (600 mg, 55.35%), as a thick mass: C₉H₁₅FO₄: ¹H NMR indicates oneenantiomer selectively formed; C-1 stereochemistry not determined: ¹HNMR (500 MHz, CDCl₃): δ 5.98 (d, J=3.5 Hz, 1H), 5.08 (dd, J=50.3, 2.3Hz, 1H), 4.70 (dd, J=13.5, 4.0 Hz, 1H), 4.10 (m, 1H), 3.97 (ddd, J=29.8,8.0, 2.3 Hz, 1H), 1.77 (d, J=5.0 Hz, 1H), 1.50 (s, 3H), 1.38 (d, J=6.5Hz, 3H), 1.33 (s, 3H).

Step-2:1-((3aR,5R,6R,6aS)-6-Fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethan-1-one(60S)

To a solution of1-((3aR,5R,6S,6aS)-6-fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethan-1-ol(59S) (100 mg, 0.48 mmol) and Ac₂O (0.1 mL) in CH₂Cl₂ (10 mL) was addedpyridinium dichromate (219 mg, 0.58 mmol). The reaction mixture wasstirred at room temperature for 16 h, concentrated under vacuum andEtOAc was added portionwise (3×100 mL) with vigorous stirring. Theorganic layers was passed through a silica-gel plug and concentrated invacuum to afford (80 mg, 80.88%) of1-((3aR,5R,6R,6aS)-6-fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethan-1-one(60S) as an colorless oil that was used without any furtherpurification. C₉H₁₃FO₄: ¹H NMR (400 MHz, CDCl₃): δ 6.13 (d, J=4.0 Hz,1H), 5.18 (dd, J=49.8, 2.6 Hz, 1H), 4.72 (dd, J=9.8, 3.8 Hz, 1H), 4.64(dd, J=33.0, 2.6 Hz, 1H), 2.28 (d, J=0.4 Hz, 3H), 1.49 (s, 3H), 1.35 (s,3H).

Step-3:2-((3aR,5R,6S,6aS)-6-Fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propan-2-ol(61S)

To a solution of1-((3aR,5R,6R,6aS)-6-fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)ethan-1-one(60S) (100 mg, 0.49 mmol) in THE (10 mL) was added methyl magnesiumbromide (1M in THF, 0.75 mL, 0.73 mmol) at −20° C. under argon. Thereaction was then stirred at room temperature for 16 h. The reactionmixture was quenched with a saturated aq. NH₄Cl solution and extractedwith EtOAc (3×50 mL). The combined organic layers were dried over anh.Na₂SO₄, filtered and concentrated in vacuo to afford the crude productwhich was purified by column chromatography on silica gel (1:4 EtOAc inpet-ether) to afford (50 mg, 46.4%) of2-((3aR,5R,6S,6aS)-6-fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propan-2-ol(61S), as an colourless oil. C₁₀H₁₇FO₄: ¹H NMR (500 MHz, CDCl₃): δ 6.04(d, J=4.0 Hz, 1H), 5.03 (dd, J=50.3, 2.3 Hz, 1H), 4.68 (dd, J=12.3, 3.8Hz, 1H), 3.99 (dd, J=34.0, 2.5 Hz, 1H), 2.18 (d, J=5.0 Hz, 1H), 1.50 (s,3H), 1.37 (s, 3H) 1.35 (s, 3H), 1.34 (s, 3H).

Step-4:2-((3aR,5R,6S,6aS)-6-Fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propan-2-yl2,2,2-trifluoroacetate (62S)

To a solution of2-((3aR,5R,6S,6aS)-6-fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propan-2-ol(61S) (1.0 g, 4.54 mmol) in CH₂Cl₂ (20 mL) was added Et₃N (1.28 mL, 9.09mmol) at 0° C. After stirring for 10 min trifluoroacetic anhydride (1.43mL, 6.81 mmol) was added at 0° C. and the reaction mixture was stirredat room temperature for an additional 16 h. Then the reaction mixturewas quenched with sat. aq. NaHCO₃ solution and extracted with CH₂Cl₂(3×100 mL). The combined organic layers were dried over Na₂SO₄, filteredand concentrated in vacuo to afford a residue that was purified bycolumn chromatography on silica gel (1:4 EtOAc in pet-ether) to afford(500 mg, 34.8%) of2-((3aR,5R,6S,6aS)-6-fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propan-2-yl2,2,2-trifluoroacetate (62S), as a colorless oil. C₁₂H₁₆F₄O₅: ¹H NMR(400 MHz, CDCl₃): δ 6.03 (d, J=4.0 Hz, 1H), 5.01 (dd, J=50.4, 2.4 Hz,1H), 4.67 (dd, J=11.8, 3.8 Hz, 1H), 4.43 (dd, J=32.4, 2.4 Hz, 1H), 1.72(s, 3H), 1.69 (s, 3H), 1.50 (s, 3H), 1.34 (s, 3H).

Step-5:(2S,3S,4S,5R)-4-Fluoro-5-(2-(2,2,2-trifluoroacetoxy)propan-2-yl)tetrahydrofuran-2,3-diyldiacetate (63S)

To2-((3aR,5R,6S,6aS)-6-fluoro-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propan-2-yl2,2,2-trifluoroacetate (62S) (800 mg, 2.53 mmol) dissolved in CH₂Cl₂ (20mL) was added AcOH (1.46 mL, 25.32 mmol), Ac₂O (1.20 mL, 12.65 mmol) andconc. H₂SO₄ (0.1 mL) at 0° C. The resulting reaction mixture was stirredat room temperature for 3 h, quenched with sat. aq. NaHCO₃ and extractedwith CH₂Cl₂ (3×100 mL). The combined organic layers were dried overNa₂SO₄, filtered and concentrated in vacuum. The residue was purified byflash chromatography (SiO₂, 0-15% EtOAc-pet. ether) to afford (150 mg,22.6%) of(2S,3S,4S,5R)-4-fluoro-5-(2-(2,2,2-trifluoroacetoxy)propan-2-yl)tetrahydrofuran-2,3-diyldiacetate (63S) as a colorless oil. C₁₃H₁₆F₄O₇: ¹H NMR (400 MHz, CDCl₃):δ 6.20 (s, 1H), 5.31 (d, J=11.6 Hz, 1H), 5.06 (d, J=50.4 Hz, 1H), 4.54(d, J=31.6 Hz, 1H), 2.14 (s, 3H), 2.10 (s, 3H), 1.74 (s, 3H), 1.69 (s,3H).

Step-6:2-((2R,3S,4S,5R)-5-(2-Acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxy-3-fluorotetrahydrofuran-2-yl)propan-2-yl2,2,2-trifluoroacetate (32)

N-(6,8-dioxo-7-(prop-2-yn-1-yl)-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide(6) (300 mg, 1.21 mmol),(2S,3S,4S,5R)-4-fluoro-5-(2-(2,2,2-trifluoroacetoxy)propan-2-yl)tetrahydrofuran-2,3-diyldiacetate (63S) (654 mg, 1.82 mmol) and BSA (0.61 mL, 3.03 mmol) weredissolved in 1,2-dichloroethane (10 mL) and the reaction mixture wasstirred at 80° C. for 30 min under argon. The reaction mixture wasallowed to cool to room temperature followed by addition of TMSOTf (0.40mL, 1.82 mmol). The resulting reaction mixture was stirred at 80° C. for30 min under argon, allowed to cool to room temperature and the solventwas removed by vacuum. The residue was dissolved in MeCN (15 mL)followed by addition of TMSOTf (0.40 mL, 1.82 mmol). The reactionmixture was heated at 80° C. for 16 h, cooled to room temperature,diluted with water and extracted with EtOAc (3×100 mL). The combinedorganic layer was washed with water (100 mL), brine (100 mL), dried overNa₂SO₄, filtered and concentrated. The crude product was purified byGRACE reverse phase flash chromatography (Column: FLASH PURE-C18 (40 mirregular), Mobile phase: 0.1% HCO₂H in H₂O:MeCN T % B):—30 mins; FlowRate: 12 mL/min.) to afford (160 mg, 24.1%) of2-((2R,3R,4S,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxy-3-fluorotetrahydrofuran-2-yl)propan-2-yl2,2,2-trifluoroacetate (32) as a yellow solid. C₂₁H₂F₄N₅O₈: ¹H NMR (400MHz, CDCl₃): δ 11.97 (bs, 1H), 8.18 (s, 1H), 6.19 (dd, J=22.8, 5.2 Hz,1H), 5.77 (d, J=5.6 Hz, 1H), 5.17 (d, J=51.4, 3.8 Hz, 1H), 4.86 (d,J=2.4 Hz, 2H), 4.27 (dd, J=29.6, 4.0 Hz, 1H), 2.32 (t, J=2.4 Hz, 1H),2.21 (s, 3H), 2.13 (s, 3H), 1.76 (s, 3H), 1.72 (s, 3H). ES+, m/z 548.40[M+H]⁺.

Step-7:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-(2-hydroxypropan-2-yl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 19

To a solution of2-((2R,3R,4S,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxy-3-fluorotetrahydrofuran-2-yl)propan-2-yl2,2,2-trifluoroacetate (32) (160 mg, 0.29 mmol) in methanol (10 mL) wasadded K₂CO₃ (48 mg, 0.35 mmol) at 0° C. The reaction mixture was stirredat room temperature for 16 h, concentrated and subjected to GRACE FLASHchromatography (Reverse phase using 0.01% of formic acid inacetonitrile). The pure fractions were concentrated to yield2-amino-9-((2R,3S,4S,5R)-4-fluoro-3-hydroxy-5-(2-hydroxypropan-2-yl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 19 (53 mg, 49.4%) as a white solid. C₁₅H₁₈FN₅O₅: ¹H NMR (400MHz, DMSO-d₆): δ 10.96 (brs, 1H), 6.56 (s, 2H), 5.93 (d, J=5.6 Hz, 1H),5.35-5.32 (m, 1H), 5.26 (m, 1H), 5.01 (ddd, J=53.8, 4.8, 2.6 Hz, 1H),4.64 (s, 1H), 4.60 (d, J=2.0 Hz, 2H), 3.75 (dd, J=26.2, 4.6 Hz, 1H),3.24 (t, J=2.2 Hz, 1H), 1.17 (s, 6H). ES+, m/z 368.0 [M+H]⁺.

Example 18:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-8H-purin-8-one,Compound 20 and2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(propa-1,2-dien-1-yl)-7,9-dihydro-8H-purin-8-one,Compound 21

Using the procedures described in Example 5, Compounds 20 and 21 weresynthesized from (21) and (37S) as follows:

Step-1:(S)-1-((2R,3S,4S,5R)-5-(2-Acetamido-8-oxo-7-(prop-2-yn-1-yl)-7,8-dihydro-9H-purin-9-yl)-4-acetoxy-3-fluorotetrahydrofuran-2-yl)propylacetate (33)

N-(8-oxo-7-(prop-2-yn-1-yl)-8,9-dihydro-7H-purin-2-yl)acetamide (21)(400 mg, 1.731 mmol),(3S,4S,5R)-5-((S)-1-acetoxypropyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate (37S) (627 mg, 2.079 mmol) and BSA (1.049 g, 5.194 mmol) weredissolved in dichloroethane (20 mL). The reaction mixture was stirred at80° C. for 30 min under argon. Then the reaction mixture wasconcentrated under reduced pressure and the residue was taken up in MeCN(50 mL). The reaction flask was charged with TMSOTf (577 mg, 2.594 mmol)and placed into a preheated oil bath at 80° C. After 18 h the reactionwas cooled to room temperature and the solvent was removed by rotaryevaporation. The resultant solid was dissolved in ethyl acetate (50 mL)and washed with saturated aqueous NaHCO₃ (2×30 mL). The organic phasewas dried over Na₂SO₄, filtered and concentrated. The crude product waspurified by column chromatography (SiO₂, 0 to 80% ethyl acetate-Petether), to yield (400 mg, 48.43%) of(S)-1-((2R,3S,4S,5R)-5-(2-acetamido-8-oxo-7-(prop-2-yn-1-yl)-7,8-dihydro-9H-purin-9-yl)-4-acetoxy-3-fluorotetrahydrofuran-2-yl)propylacetate (33) as a light yellow solid. C₂₁H₂₄FN₅O₇: ES+, m/z 477.8[M+H]+. LC/MS also indicated loss of one Ac group (ES+, m/z 435.8[M+H]+). The product was used without further purification.

Step-2:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-8H-purin-8-one,Compound 20 and2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(propa-1,2-dien-1-yl)-7,9-dihydro-8H-purin-8-one,Compound 21

(S)-1-((2R,3S,4S,5R)-5-(2-acetamido-8-oxo-7-(prop-2-yn-1-yl)-7,8-dihydro-9H-purin-9-yl)-4-acetoxy-3-fluorotetrahydrofuran-2-yl)propylacetate (33) (400 mg, 0.8385 mmol) was dissolved in methanol (10 mL)followed by addition of K₂CO₃ (173 mg, 1.257 mmol) at 0° C. The reactionmixture was stirred at room temperature for 16 h and concentrated. Theresidue was purified by GRACE FLASH chromatography (Reverse phase; 0.01%of formic acid in acetonitrile) to afford (53 mg, 38.93%) of2-amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-8H-purin-8-one(Compound 20) as an off white solid and (20 mg, 14.69%) of2-amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(propa-1,2-dien-1-yl)-7,9-dihydro-8H-purin-8-one(Compound 21) as an off white solid.

Compound 20: C₁₅H₁₈FN₅O₄: ES+, m/z 352.2 [M+H]⁺; ¹H NMR (500 MHz,DMSO-d₆): δ 8.06 (s, 1H), 6.39 (s, 2H), 5.97 (d, J=5.5 Hz, 1H), 5.46 (d,J=6.5 Hz, 1H), 5.40 (m, 1H), 5.00 (ddd, J=53.3, 4.3, 2.0 Hz, 1H), 4.80(d, J=6.5 Hz, 1H), 4.66 (d, J=5.5 Hz, 2H), 3.85 (ddd, J=24.3, 7.0, 4.8Hz, 1H), 3.56 (m, 1H), 3.41 (t, J=2.5 Hz, 1H), 1.49 (m, 1H), 1.35 (m,1H), 0.91 (t, J=7.3 Hz, 3H).

Compound 21: C₁₅H₁₈FN₅O₄: ES+, m/z 352.1 [M+H]⁺; ¹H NMR (500 MHz,DMSO-d₆): δ 8.18 (s, 1H), 7.23 (t, J=6.8 Hz, 1H), 6.52 (s, 2H), 5.95(brs, 1H), 5.83 (d, J=6.5 Hz, 2H), 5.48 (d, J=6.0 Hz, 1H), 5.33 (ddd,J=25.0, 6.0, 2.0 Hz, 1H), 5.01 (ddd, J=53.0, 4.5, 2.0 Hz, 1H), 4.77 (s,1H), 3.85 (ddd, J=24.3, 7.3, 4.5 Hz, 1H), 3.57 (m, 1H), 1.51 (m, 1H),1.34 (m, 1H), 0.92 (t, J=7.3 Hz, 3H).

Example 19:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(2-(methylthio)ethyl)-7,9-dihydro-1H-purine-6,8-dione,Compound 22

Compound 22 was prepared according to the following multi-stepprocedure.

Step-1:2-Amino-6-(benzyloxy)-9-(4-methoxybenzyl)-7-(2-(methylthio)ethyl)-7,9-dihydro-8H-purin-8-one(34)

To a suspension of2-amino-6-(benzyloxy)-9-(4-methoxybenzyl)-7,9-dihydro-8H-purin-8-one(4.0 g, 10.61 mmol) (3) in DMF (60 mL) was added(2-chloroethyl)(methyl)sulfane (2.56 g, 23.34 mmol), K₂CO₃ (4.39 g,31.83 mmol) at 0° C. The reaction mixture was stirred at 70° C. for 16h. The reaction mixture was quenched with ice water (200 mL), diethylether (100 mL) was added and stirred for 15 min. The resultingprecipitated solid was filtered, washed with water and dried to give2-amino-6-(benzyloxy)-9-(4-methoxybenzyl)-7-(2-(methylthio)ethyl)-7,9-dihydro-8H-purin-8-one(34) (4.0 g, 85%) as an off-white solid. C₂₃H₂₅N₅O₃S: ¹H NMR (400 MHz,DMSO-d₆): δ 7.47 (d, J=7.2 Hz, 1H), 7.40 (d, J=6.8 Hz, 2H), 7.39-7.22(m, 2H), 7.19 (d, J=6.8 Hz, 2H), 6.87 (d, J=8.8 Hz, 2H), 6.42 (s, 2H),5.42 (s, 2H), 4.83 (s, 2H), 3.93 (t, J=7.0 Hz, 2H), 3.71 (s, 3H), 2.68(t, J=7.0 Hz, 2H), 1.90 (s, 3H). ES+, m/z 452.3 [M+H]⁺.

Step-2:2-Amino-6-(benzyloxy)-7-(2-(methylthio)ethyl)-7,9-dihydro-8H-purin-8-one(35)

Trifluoromethane sulfonic acid (3.56 mL, 35.47 mmol) was added to asuspension of2-amino-6-(benzyloxy)-9-(4-methoxybenzyl)-7-(2-(methylthio)ethyl)-7,9-dihydro-8H-purin-8-one(34) (4.0 g, 8.86 mmol) in TFA (2.71 mL, 35.47 mmol) at room temperatureunder argon atmosphere and the resulting reaction mixture was stirred atroom temperature for 16 h under argon atmosphere. The reaction mixturewas quenched with ice cold water (200 mL) and made basic with sat. aq.NaHCO₃ solution (300 mL) under vigorous stirring and filtered. Thefiltered solid was taken up in ethyl acetate, stirred for 30 min.,filtered and dried to afford2-amino-6-(benzyloxy)-7-(2-(methylthio)ethyl)-7,9-dihydro-8H-purin-8-one(35) (1.8 g, 62%) as a brown solid. C₁₅H₁₇N₅O₂S; ¹H NMR (400 MHz,DMSO-d₆): δ 10.87 (s, 1H), 7.47 (s, 5H), 6.48 (s, 2H), 4.84 (d, J=12.8Hz, 1H), 4.64 (d, J=12.8 Hz, 1H), 4.23 (m, 2H), 3.67-3.58 (m, 2H), 2.81(s, 3H). ES+, m/z 332.2 [M+H]⁺.

Step-3: 2-Amino-7-(2-(methylthio)ethyl)-7,9-dihydro-1H-purine-6,8-dione(36)

LiBr (0.701 g, 8.15 mmol) and TMSCl (2.7 mL g, 21.7 mmol) were added toa suspension of2-amino-6-(benzyloxy)-7-(2-(methylthio)ethyl)-7,9-dihydro-8H-purin-8-one(35) (1.8 g, 5.4 mmol) in acetonitrile (36 mL) at 0° C. under argonatmosphere. The reaction mixture was stirred at 50° C. for 16 h underargon atmosphere, quenched with ice cold water (200 mL), made basic withsat. aq. NaHCO₃ solution (300 mL) with vigorous stirring. The solidformed was filtered and EtOAc was added, stirred for 30 min, filteredoff and dried to afford2-amino-7-(2-(methylthio)ethyl)-7,9-dihydro-1H-purine-6,8-dione (36)(1.0 g, 76%) as a brown solid. C₈H₁₁N₅O₂S: ¹H NMR (400 MHz, DMSO-d₆): δ11.09 (s, 1H), 10.66 (s, 1H), 6.37 (s, 2H), 3.90 (t, J=6.8 Hz, 2H), 2.76(t, J=6.8 Hz, 2H), 2.07 (s, 3H). ES+, m/z 242.0 [M+H]⁺.

Step-4:N-(7-(2-(Methylthio)ethyl)-6,8-dioxo-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide(37)

Acetic anhydride (2.53 mL, 24.89 mmol) was added to a solution of2-amino-7-(2-(methylthio)ethyl)-7,9-dihydro-1H-purine-6,8-dione (36) (1g, 4.14 mmol) in AcOH (10 mL) at ambient temperature under argonatmosphere and the resulting reaction mixture was heated at 120° C. for16 h under argon atmosphere. The reaction mixture was stirred and cooledto 0° C. for 30 minutes whereupon a dark solid precipitated. The productwas filtered, washed with diethyl ether and dried under vacuum to affordN-(7-(2-(methylthio)ethyl)-6,8-dioxo-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide(37) (1.0 g, 85%) as an brown solid. The dried product was directly usedin the next step. C₁₀H₁₃N₅O₃S: ¹H NMR (500 MHz, DMSO-d₆): δ 12.01 (s,1H), 11.69 (s, 1H), 11.64 (s, 1H), 3.99 (t, J=7.0 Hz, 2H), 2.79 (t,J=7.0 Hz, 2H), 2.18 (s, 3H), 2.08 (s, 3H). ES+, m/z 283.8 [M+H]⁺.

Step-5:(S)-1-((2S,4R,5R)-5-(2-Acetamido-7-(2-(methylthio)ethyl)-6,8-dioxo-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)propylacetate (38)

N-(7-(2-(methylthio)ethyl)-6,8-dioxo-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide(37) (760 mg, 2.663 mmol),(3R,5S)-5-((S)-1-acetoxypropyl)tetrahydrofuran-2,3-diyl diacetate (14S)(923 mg, 3.20 mmol) and BSA (1.33 mL, 5.28 mmol) were dissolved in1,2-dichloroethane (35 mL) and the resulting reaction mixture wasstirred at 80° C. for 30 min under argon. The reaction mixture wasallowed to cool to rt and 1,2-dichloroethane was removed under vacuum.The residue was dissolved in MeCN (35 mL) followed by addition of TMSOTf(0.488 mL, 2.64 mmol). The reaction mixture was heated at 80° C. for 16h, cooled to room temperature and concentrated under vacuum. The residuewas diluted with sat. aq. NaHCO₃ (60 mL) and extracted with EtOAc (3×80mL). The combined EtOAc layer was washed with water (50 mL), brine (40mL), dried over Na₂SO₄, filtered and concentrated under vacuum. Thecrude compound was purified by flash column chromatography on silica gel(80% EtOAc in pet. ether) to afford(S)-1-((2S,4R,5R)-5-(2-acetamido-7-(2-(methylthio)ethyl)-6,8-dioxo-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)propylacetate (38) (250 mg, 28%) as an off-white solid and taken on directlyto the final step as is.

Step-6:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(2-(methylthio)ethyl)-7,9-dihydro-1H-purine-6,8-dione,Compound 22

To a solution of(S)-1-((2S,4R,5R)-5-(2-acetamido-7-(2-(methylthio)ethyl)-6,8-dioxo-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)propylacetate (38) (250 mg, 0.4892 mmol) in methanol (10 mL), was added K₂CO₃(135 mg, 0.978 mmol) at room temperature. The reaction was monitored byLC/MS until (38) was consumed. After stirring at room temperature for 16h. the reaction mixture was concentrated under vacuum to afford a crudesolid that was purified by GRACE reverse phase chromatography (0.1% aq.HCO₂H:MeCN) to give2-amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(2-(methylthio)ethyl)-7,9-dihydro-1H-purine-6,8-dione(Compound 22) (25 mg, 14%) as an off-white solid. C₁₅H₂₃N₅O₅S: ¹H NMR(500 MHz, DMSO-d₆): δ 11.6 (s, 1H), 6.62 (s, 2H), 5.52 (d, J=3.5 Hz,1H), 5.35 (d, J=4.5 Hz, 1H), 4.75 (m, 2H), 4.00 (m, 1H), 3.95 (t, J=7.0Hz, 2H), 3.25 (m, 1H), 2.78 (t, J=7.0 Hz, 2H), 2.38 (m, 1H), 2.08 (s,3H), 1.78 (m, 1H), 1.39 (m, 1H), 1.28 (m, 1H), 0.87 (t, J=7.5 Hz, 3H).ES+, m/z 386.2 [M+H]⁺.

Example20:2-Amino-9-((2R,3R,5S)-5-((S)-2-fluoro-1-hydroxyethyl)-3-hydroxytetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 23

Compound 23 was prepared according to the following multi-stepprocedure.

Step-1:(S)-1-((3aR,5S,6aR)-2,2-Dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)-2-fluoroethylacetate (64S)

A 40% HF solution (0.69 mL, 16.1 m·mol) was added to TBAF (1M in THF)(16 mL, 16.1 mmol) and after 5 min the solution was concentrated underreduced pressure (1 mbar, 100° C.). To this concentrated mixture,(3aR,5S,6aR)-2,2-dimethyl-5-((R)-oxiran-2-yl)tetrahydrofuro[2,3-d][1,3]dioxole(9S) (1 g, 5.3 mmol), and a solution of KHF₂ (125.8 mg, 1.61 mmol) indry toluene (20 ml) were added and the mixture was maintained at 120° C.for 18 h. The reaction mixture was cooled to rt, Ac₂O (1.6 mL, 16.1mmol) and dry pyridine (3.5 mL, 16.1 mmol) were added and the mixturewas maintained under stirring at 40° C. for 2 h. The reaction mixturewas quenched with water and extracted with EtOAc (2×75 mL). The organicphase was washed with 2M HCl and saturated aq. NaHCO₃ solution (50 mL),dried over anhydrous Na₂SO₄, filtered and concentrated under vacuum. Thecrude product was purified by column chromatography on silica gel(100-200 mesh, 20% EtOAc in petroleum ether) to afford 1 g (76%) of(S)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)-2-fluoroethylacetate (64S). C₁₁H₁₇FO₅: ¹H NMR (400 MHz, CDCl3): δ 5.80 (d, J=3.6 Hz,1H), 5.11 (m, 1H), 4.74 (t, J=4.2 Hz, 1H), 4.61 (ddd, J=47.6, 10.6, 3.0Hz, 1H), overlapping with 4.56 (ddd, J=46.8, 10.6, 4.8 Hz, 1H), 4.36(ddd, J=10.6, 6.2, 4.8 Hz, 1H), 2.17 (dd, J=13.6, 4.4 Hz, 1H), 2.11 (s,3H), 1.80 (dd, J=13.4, 10.6, 4.8 Hz, 1H), 1.51 (s, 3H), 1.32 (s, 3H).

Step-2: (3R,5S)-5-((S)-1-Acetoxy-2-fluoroethyl)tetrahydrofuran-2,3-diyldiacetate (65S)

To a solution of(S)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)-2-fluoroethylacetate (64S) (1 g, 4.03 mmol), acetic acid (2.3 mL, 40.3 mmol) andacetic anhydride (2 mL, 20.1 mmol) in anhydrous CH₂Cl₂ (30 mL) was addedconcentrated H₂SO₄ (0.1 mL) at 0° C. After being stirred at 25° C. for 4h, the reaction was quenched by the addition of ice cold water. Theorganic layer was separated and the aqueous phase was extracted withCH₂Cl₂ (2×75 mL). The combined organic layer was washed with saturatedaq·NaHCO₃ solution (50 mL), dried over Na₂SO₄, filtered and concentratedunder vacuum. The crude product was purified by column chromatography onsilica gel (100-200 mesh, 30% EtOAc in petroleum ether) to afford 0.4 g(36%) of (3R,5S)-5-((S)-1-acetoxypropyl)tetrahydrofuran-2,3-diyldiacetate (64S) as a colorless oil. C₁₂H₁₇FO₇: ¹H NMR indicated an α(minor), β (major) anomeric mixture; ¹H NMR (400 MHz, CDCl₃): δ 6.16 (s,1H), 5.18 (m, 1H), 5.08-5.02 (m, 1H), 4.66-4.64 (m, 1H), 4.55-4.51 (m,2H), 2.23-2.12 (m, 2H), 2.10-2.08 (m, 9H).

Step-3:(S)-1-((2S,4R,5R)-5-(2-Acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2-fluoroethylacetate (39)

N-(6,8-Dioxo-7-(prop-2-yn-1-yl)-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide(6) (250 mg, 1.01 mmol),(3R,5S)-5-((S)-1-acetoxypropyl)tetrahydrofuran-2,3-diyl diacetate (64S)(354.6 mg, 1.2 mmol), and BSA (0.76 mL, 3.03 mmol) were dissolved in1,2-dichloroethane (15 mL) and the solution was stirred at 80° C. for 30min under argon. The reaction mixture was then cooled to rt and1,2-dichloroethane was removed under vacuum. The residue was dissolvedin MeCN (20 mL) followed by the addition of TMSOTf (0.28 mL, 1.5 mmol).The reaction mixture was heated at 80° C. for 16 h., cooled to roomtemperature and concentrated under vacuum. The residue was diluted withsat. aq. NaHCO₃ (50 mL) and extracted with EtOAc (3×50 mL). The combinedEtOAc layer was washed with water (30 mL), brine (30 mL), dried overNa₂SO₄, filtered and concentrated under vacuum. The crude compound waspurified by GRACE flash chromatography (80% EtOAc in Pet ether) toafford 190 mg (39%) of(S)-1-((2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2-fluoroethylacetate (39) as an off-white solid. C₂₀H₂₂FN₅O₈: ES+, m/z 480.2 [M+H]⁺.

Step-4:2-Amino-9-((2R,3R,5S)-5-((S)-2-fluoro-1-hydroxyethyl)-3-hydroxytetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 23

To a solution of(S)-1-((2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2-fluoroethylacetate (39) (190 mg, 0.39 mmol) in MeOH (10 mL) was added K₂CO₃ (54.7mg, 0.43 mmol) at 0° C., and the reaction mixture was stirred at RT for16 h. The solvent was removed under reduced pressure at RT and theresidue was purified by Prep-HPLC (Column: X-select-C18 (250*19), 5 uMobile phase: 10 mM ammonium bicarbonate in H₂O:MeCN Gradient: (T %B):—0/5, 1/5, 8/50, 8.1/98, 11/98, 11.1/5, 14/5 Flow rate: 18 mL/minDiluent: MeCN+H₂O+THF). The pure fractions were lyophilized to afford 55mg (39%) of2-amino-9-((2R,3R,5S)-5-((S)-2-fluoro-1-hydroxyethyl)-3-hydroxytetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione(Compound 23) as an off white solid. C₁₄H₁₆FN₅O₅: ¹H NMR (400 MHz,DMSO-d₆): δ 11.09 (brs, 1H), 6.59 (bs, 2H) 5.52 (d, J=3.6 Hz, 1H), 5.43(d, J=4.8 Hz, 1H), 5.28 (d, J=5.6 Hz, 1H), 4.80 (m, 1H), 4.58 (d, J 2.4Hz, 2H), 4.49-4.36 (m, 1H), 4.38-4.22 (m, 1H), 4.05 (q, J=7.2 Hz, 1H),3.77-3.70 (m, 1H), 3.22 (t, J=2.2 Hz, 1H), 2.55 (m, 1H), 1.93 (m, 1H).ES+, m/z 354.1 [M+H]⁺.

Example 21:2-Amino-9-((2R,3R,5S)-5-((R)-2-fluoro-1-hydroxyethyl)-3-hydroxytetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 24

Similar to the procedure used to synthesize Compound 23, Compound 24 wasprepared according to the following multi-step procedure.

Step-1:(R)-1-((3aR,5S,6aR)-2,2-Dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)-2-fluoroethylacetate (66S)

A 40% HF solution (1.38 mL, 32.2 mmol) was added to TBAF (32 mL, 32.2mmol 1M in THF) and after 5 min the solution was concentrated underreduced pressure (1 mbar, 100° C.). To this concentrated mixture asolution of(3aR,5S,6aR)-2,2-dimethyl-5-((S)-oxiran-2-yl)tetrahydrofuro[2,3-d][1,3]dioxole(51S) (2 g, 10.7 mmol) and KHF₂ (251.6 mg, 3.2 mmol) in dry toluene (20mL) were added and the mixture was maintained at 120° C. for 18 h. Thereaction mixture was then cooled to room temperature and Ac₂O (3.2 mL,32.2 mmol) and dry pyridine (6.1 mL, 86.0 mmol) were added. The reactionmixture was stirred at 40° C. for 2 h and then quenched with water andEtOAc (2×75 mL). The combined organic phase was washed with 2M HCl, asaturated aq. NaHCO₃ solution (50 mL), dried over Na₂SO₄, filtered andconcentrated under vacuum. The crude mixture was purified by columnchromatography over silica gel (100-200 mesh, 20% EtOAc in petroleumether) to give 1.6 g (61%) of(R)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)-2-fluoroethylacetate (66S). C₁₁H₁₇FO₅: ¹H NMR (400 MHz, CDCl₃): δ 5.82 (d, J=3.6 Hz,1H), 5.19-5.14 (m, 1H), 4.74 (t, J 4.2 Hz, 1H), 4.63 (m, 1H), 4.51 (m,1H), 4.41 (dt, J=10.8, 4.6 Hz, 1H), 2.14 (s, 3H), 2.11 (m, 1H) 1.66(ddd, J=13.2, 10.8, 4.8 Hz, 1H), 1.51 (s, 3H), 1.32 (s, 3H).

Step-2: (3R,5S)-5-((R)-1-Acetoxy-2-fluoroethyl)tetrahydrofuran-2,3-diyldiacetate (67S)

To a solution of(R)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)-2-fluoroethylacetate (66S) (1.6 g, 4.03 mmol), acetic acid (3.6 mL, 64.5 mmol) andacetic anhydride (3.2 mL, 32.2 mmol) in anhydrous CH₂Cl₂ (20 mL) wasadded concentrated H₂SO₄ (0.1 mL) at 0° C. The resultant reactionmixture was stirred at 22° C. for 4 h and was then quenched by theaddition of ice cold water. The organic layer was separated and theaqueous phase was extracted with CH₂Cl₂ (2×75 mL). The combined organiclayer was washed with saturated aq. NaHCO₃ solution (50 mL), dried overNa₂SO₄, filtered and concentrated under vacuum. The crude product waspurified by column chromatography over silica gel (100-200 mesh, 30%EtOAc in petroleum ether) to give 0.8 g (44%) of(3R,5S)-5-((R)-1-acetoxy-2-fluoroethyl)tetrahydrofuran-2,3-diyldiacetate (67S) as a colorless oil. C₁₂H₁₇FO₇: ¹H NMR indicated an α(minor), β (major) anomeric mixture; ¹H NMR (400 MHz, CDCl₃): δ 6.13 (s,1H), 5.20 (d, J=4.4 Hz, 2H), 5.12 (ddd, J=20.4, 4.4, 1.3 Hz, 1H),4.61-4.47 (m, 4H), 2.14 (s, 3H), 2.10 (s, 3H), 2.08 (s, 3H).

Step-3:(R)-1-((2S,4R,5R)-5-(2-Acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2-fluoroethylacetate (40)

N-(6,8-dioxo-7-(prop-2-yn-1-yl)-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide(6) (300 mg, 1.2 mmol),(3R,5S)-5-((R)-1-acetoxy-2-fluoroethyl)tetrahydrofuran-2,3-diyldiacetate (67S) (425.5 mg, 1.4 mmol) and BSA (0.9 mL, 3.6 mmol) weredissolved in 1,2-dichloroethane (15 mL) and stirred at 80° C. for 30 minunder argon. The reaction mixture was allowed to cooled to RT and1,2-dichloroethane was removed in vacuo. The residue was dissolved inMeCN (20 mL) and to the solution was added TMSOTf (0.33 mL, 1.5 mmol).The reaction mixture was stirred at 80° C. for 16 h, cooled to roomtemperature and concentrated under vacuum. To the residue was added sat.aq·NaHCO₃ (50 mL) and extracted with EtOAc (3×50 mL). The combined EtOAclayer was washed with water (30 mL), brine (30 mL), dried over anhydrousNa₂SO₄, filtered and concentrated under vacuum. The crude compound waspurified by GRACE flash chromatography (80% EtOAc in pet ether) toafford 120 mg (20%) of(R)-1-((2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2-fluoroethylacetate (40) as an off-white solid. C₂H₂₂FN₅O₈: ES+, m/z 480.2 [M+H]⁺.

Step-4:2-amino-9-((2R,3R,5S)-5-((R)-2-Fluoro-1-hydroxyethyl)-3-hydroxytetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,(Compound 24)

To a solution of(R)-1-((2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2-fluoroethylacetate (40) (120 mg, 0.25 mmol) in MeOH (10 mL) was added K₂CO₃ (34.5mg, 0.43 mmol) at 0° C. The reaction mixture was stirred at RT for 16 hand then the solvent was removed under reduced pressure at RT. Theresidue was purified by Prep HPLC (Column: X-Select-C18 (150*19), 5 uMobile phase: 0.1% HCO₂H in H₂O:MeCN Gradient: (T % B):—0/5, 8/40,8.1/98, 10/98, 10.1/5, 12/5 Flow Rate: 17 mL/min; Diluent: MeOH+H₂O+THF)and the pure fractions were lyophilized to afford 35 mg (39%) of2-amino-9-((2R,3R,5S)-5-((R)-2-fluoro-1-hydroxyethyl)-3-hydroxytetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione(Compound 24) as an off white solid. C₁₄H₁₆FN₅O₅: ¹H NMR (400 MHz,DMSO-d₆): δ 11.36 (brs, 1H), 6.69 (s, 2H), 5.53 (d, J=2.8 Hz, 1H), 5.46(brs, 1H), 5.24 (m, 1H), 4.73 (m, 1H), 4.59 (brs, 2H), 4.48-4.39 (m,1H), 4.36-4.27 (m, 1H), 4.16 (m, 1H), 3.71-3.67 (m, 1H), 3.22 (s, 1H),2.45 (m, 1H), 1.83 (m, 1H). ¹⁹F NMR (376 MHz, DMSO-d₆): δ-228.9 (ddd,J=47.4, 46.2, 19.4 Hz). ES+, m/z 354.1 [M+H]⁺.

Example22:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-propyl-7,9-dihydro-1H-purine-6,8-dione,Compound 25

Compound 25 was prepared according to the following multi-stepprocedure.

Step-1:2-Amino-6-(benzyloxy)-9-(4-methoxybenzyl)-7-propyl-7,9-dihydro-8H-purin-8-one(41)

1-Iodopropane (1.59 mL, 15.91 mmol) was added to a suspension of2-amino-6-(benzyloxy)-9-(4-methoxybenzyl)-7,9-dihydro-8H-purin-8-one (3)(4 g, 10.61 mmol), K₂CO₃ (3.66 g, 26.52 mmol) in DMF (50 mL) at 0° C.and stirred at room temperature for 16 h. The reaction mixture wasquenched with ice water (100 mL), diluted with diethyl ether (80 mL) andstirred for 15 min. The resulting precipitate was collected byfiltration, washed with water and dried to afford2-amino-6-(benzyloxy)-9-(4-methoxybenzyl)-7-propyl-7,9-dihydro-8H-purin-8-one(41) (3.5 g, 75%) as an brown solid; C₂₃H₂₅N₅O₃: ¹H NMR (400 MHz,DMSO-d₆): δ 7.48-7.34 (m, 5H), 7.20 (d, J=8.8 Hz, 2H), 6.87 (d, J=8.8Hz, 2H), 6.39 (s, 2H), 5.41 (s, 2H), 4.82 (s, 2H), 3.73-3.69 (m, 2H),3.71 (s, 3H), 1.58 (m, 2H), 0.73 (t, J=7.4 Hz, 3H). ES+, m/z 420.2[M+H]⁺.

Step-2: 2-Amino-7-propyl-7,9-dihydro-1H-purine-6,8-dione (42)

Trifluoromethanesulfonic acid (4 mL, 50.11 mmol) was added to asuspension of2-amino-6-(benzyloxy)-9-(4-methoxybenzyl)-7-propyl-7,9-dihydro-8H-purin-8-one(41) (3.5 g, 8.35 mmol) in trifluoroacetic acid (4.4 mL, 50.11 mmol) at0° C. under an argon atmosphere and the resulting reaction mixture wasslowly warmed to room temperature and stirred for 3 h. The reactionmixture was quenched with ice cold water, the pH was made basic withexcess sat. aq. NaHCO₃ under vigorous stirring and filtered. Theresidual solid was taken into diethyl ether (150 mL), stirred for 30min, filtered and dried to afford2-amino-7-propyl-7,9-dihydro-1H-purine-6,8-dione (42) (1.6 g; 91%) as apale yellow solid: C₈H₁₁N₅O₂: ¹H NMR (400 MHz, DMSO-d₆): δ 11.04 (s,1H), 10.64 (s, 1H), 6.33 (s, 2H), 3.67 (t, J=7.2 Hz, 2H), 1.62 (sextet,J=7.2 Hz, 2H), 0.81 (t, J=7.6 Hz, 3H). ES+, m/z 210.1 [M+H]⁺.

Step-3: N-(6,8-Dioxo-7-propyl-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide(43)

Acetic anhydride (2.27 mL, 22.96 mmol) was added to a solution of2-amino-7-propyl-7,9-dihydro-1H-purine-6,8-dione (42) (1.6 g, 7.65 mmol)in AcOH (20 mL) at ambient temperature under argon atmosphere and theresulting reaction mixture was heated at 120° C. for 10 h. Withvigourous stirring reaction mixture was cooled to 0° C. whereupon asolid was formed. After stirring at 0° C. for an additional 30 minutes,the solids were filtered and dried under vacuum to affordN-(6,8-dioxo-7-propyl-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide (43)(1.3 g, 68%) as a pale yellow solid: C₁₀H₁₃N₅O₃: ¹H NMR (400 MHz,DMSO-d₆): δ 11.98 (s, 1H), 11.65 (s, 1H), 11.64 (s, 1H), 3.76 (t, J=7.0Hz, 2H), 2.15 (s, 3H), 1.67-1.62 (m, 2H), 0.83 (t, J=7.4 Hz, 3H). ES+,m/z 252.1 [M+H]⁺.

Step-4:(R)-1-((2S,4R,5R)-5-(2-Acetamido-6,8-dioxo-7-propyl-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2,2,2-trifluoroethylacetate (44A)

N-(6,8-Dioxo-7-propyl-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide (43)(500 mg, 1.99 mmol),(2S,3R,5S)-5-(1-acetoxy-2,2,2-trifluoroethyl)tetrahydrofuran-2,3-diyldiacetate (22S) (784 mg, 2.39 mmol), BSA (1.5 mL, 5.97 mmol) weredissolved in 1,2-dichloroethane (20 mL) and the resulting reactionmixture was stirred at 80° C. for 30 min under argon. The reactionmixture was allowed to cool to RT and 1,2-dichloroethane was removedunder vacuum. The residue was dissolved in MeCN (20 mL) followed by theaddition of TMSOTf (0.54 mL, 2.98 mmol). With stirring, the reactionmixture was heated at 80° C. for 16 h, cooled to room temperature andconcentrated under vacuum. To the residue was added sat. aq·NaHCO₃ (50mL) and extracted with EtOAc (3×50 mL). The combined EtOAc layers werewashed with water (30 mL), brine (30 mL), dried over Na₂SO₄, filteredand concentrated under vacuum. The crude compound was purified by GRACEflash chromatography (80% EtOAc in pet ether) to afford 400 mg ofdiastereomeric mixture as indicated by LC/MS (estimated to be ˜3:144A:44B) Further purification by Prep-HPLC (KROMOSIL-C18 (150*25 MM), 7u Mobile phase: 10 mM ammonium bicarbonate in H₂O:MeCN gradient: (T %B):—0/20, 8/50, 13/50, 13.1/98, 15/98, 15.1/20, 17/20; Flow Rate: 22mL/min; Diluent: (MeCN+H₂O+THF) gave ˜100 mg of(R)-1-((2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-propyl-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2,2,2-trifluoroethylacetate (44A) and ˜50 mg of(S)-1-((2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-propyl-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2,2,2-trifluoroethylacetate (44B), both as pale yellow solids after lyophilization. (44A):C₂₀H₂₄F₃N₅O₈: ¹H NMR (500 MHz, DMSO-d₆): δ 12.15 (brs, 1H), 11.75 (brs,1H), 5.75 (d, J=1.5 Hz, 1H), 5.66 (m, 2H), 4.51 (m, 1H), 3.82 (t, J=7.0Hz, 2H), 2.84 (m, 1H), 2.17 (s, 3H), 2.13 (m, 1H), 2.08 (s, 6H), 1.67(m, 2H), 0.85 (t, J=7.5 Hz, 3H). ES+, m/z 520.1 [M+H]⁺. (44B): ¹H NMR(500 MHz, CDCl₃): δ 11.96 (brs, 1H), 9.50 (brs, 1H), 6.16 (s, 1H), 6.02(t, J=7.0 Hz, 1H), 5.41 (d, J=4.5 Hz, 1H), 4.65 (m, 1H), 3.97 (t, J=7.3Hz, 2H), 2.94 (m, 1H), 2.29 (s, 3H), 2.25 (s, 3H), 2.16 (m, 1H), 2.14(s, 6H) 1.77 (m, 2H), 0.94 (t, J=7.0 Hz, 3H).

Step-5:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-propyl-7,9-dihydro-1H-purine-6,8-dione(Compound 25)

To a solution of(R)-1-((2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-propyl-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2,2,2-trifluoroethylacetate (44A) (100 mg, 0.192 mmol) in MeOH (20 mL) was added K₂CO₃ (40mg, 0.289 mmol) at 0° C. and the reaction mixture was stirred at rt for16 h. Methanol was removed under reduced pressure at 30° C. The residuewas purified by reverse phase GRACE flash chromatography (using 10 mMammonium bicarbonate in H₂O as eluent). The pure fractions werelyophilized to afford 60 mg (80%) of2-amino-9-((2R,3R,5S)-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-propyl-7,9-dihydro-1H-purine-6,8-dione (Compound25) as a white solid. C₁₄H₁₈F₃N₅O₅: ¹H NMR (500 MHz, DMSO-d₆): δ 11.06(brs, 1H), 6.53 (brs, 2H), 6.39 (d, J=8.0 Hz, 1H), 5.58 (d, J=3.50 Hz,1H), 5.52 (d, J=4.5 Hz, 1H), 4.76 (m, 1H), 4.34 (m, 1H), 4.02 (m, 1H),3.74 (t, J=7.3 Hz, 2H), 2.54 (m, 1H), 1.97 (m, 1H), 1.63 (sextet, J=7.3Hz, 2H), 0.82 (t, J=7.3 Hz, 3H). ES+, m/z 394.0 [M+H]⁺.

Example23:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-propyl-7,9-dihydro-1H-purine-6,8-dione,Compound 26

Compound 26 was prepared according to the following 2 step procedure.

Step-1:(S)-1-((2R,3S,4S,5R)-5-(2-Acetamido-6,8-dioxo-7-propyl-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxy-3-fluorotetrahydrofuran-2-yl)propylacetate (45)

N-(6,8-Dioxo-7-propyl-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide (43)(300 mg, 1.1 mmol),(3S,4S,5R)-5-((S)-1-acetoxypropyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate (37S) (548.6 mg, 1.7 mmol) and BSA (0.9 mL, 3.58 mmol) weredissolved in 1,2-dichloroethane (20 mL) and the resulting reactionmixture was stirred at 80° C. for 30 min under argon. The reactionmixture was allowed to cool to RT and 1,2-dichloroethane was removedunder vacuum. The residue was dissolved in MeCN (20 mL) followed byaddition of TMSOTf (0.33 mL, 1.79 mmol). The reaction mixture was heatedat 80° C. for 16 h, was cooled to room temperature and concentratedunder vacuum. To the residue was added sat. aq. NaHCO₃ (60 mL) andextracted with EtOAc (3×60 mL). The combined EtOAc layer were washedwith water (30 mL), brine (30 mL), dried over Na₂SO₄, filtered andconcentrated under vacuum. The crude product was purified by flashcolumn chromatography (80% EtOAc in pet ether) to afford 200 mg (33%)(S)-1-((2R,3S,4S,5R)-5-(2-acetamido-6,8-dioxo-7-propyl-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxy-3-fluorotetrahydrofuran-2-yl)propylacetate (45) as an off-white solid. C₂₁H₂₈FN₅O₈: ES+, m/z 498.2 [M+H]⁺.

Step-2:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-propyl-7,9-dihydro-1H-purine-6,8-dione(Compound 26)

To a solution of(S)-1-((2R,3S,4S,5R)-5-(2-acetamido-6,8-dioxo-7-propyl-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxy-3-fluorotetrahydrofuran-2-yl)propylacetate (45) (200 mg, 0.4 mmol) in methanol (10 mL) was added K₂CO₃ (111mg, 0.80 mmol) at rt. The stirred reaction mixture was monitored byLC/MS. After 16 h. the mixture was concentrated under vacuum to afford athick mass that was subjected to Prep-HPLC (Column: LUNA@ OMEGA(250*21.2), 5 u Mobile phase: 0.1% HCO₂H in H₂O:MeCN GRADIENT: (T %B):—0/10, 8/50, 9/50, 9.1/98, 12/98, 12.1/10, 15/10 Flow Rate: 17mL/min) to afford 30 mg (21%) of2-amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-propyl-7,9-dihydro-1H-purine-6,8-dione(Compound 26) as an off-white solid; C₁₅H₂₂FN₅O₅: ¹H NMR indicated theproduct to be the formic acid salt. ¹H NMR (500 MHz, DMSO-d₆): δ 11.59(brs, 1H), 8.48 (s, 1H), 6.79 (s, 2H), 5.95 (m, 1H), 5.37 (d, J=6.5 Hz,1H) 5.32 (ddd, J=24.8, 6.5, 2.8 Hz, 1H), 5.00 (dd, J=50.5, 4.5 Hz, 1H),4.91 (m, 1H), 3.82 (dt, J=21.5, 5.8 Hz, 1H), 3.75 (t, J 7.0 Hz, 2H),3.51 (brs, 1H), 1.64 (m, 2H), 1.50-1.43 (m, 1H), 1.36-1.31 (m, 1H), 0.91(t, J 7.3 Hz, 3H), 0.84 (t, J 7.3 Hz, 3H). ES+, m/z 372.2 [M+H]⁺.

Example 24:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(3,3,3-trifluoropropyl)-7,9-dihydro-1H-purine-6,8-dione,Compound 27

Compound 27 was prepared according to the following multistep procedure.

Step-1: 3,3,3-Trifluoropropyl methanesulfonate (46)

To a solution of 3,3,3-trifluoropropan-1-ol [2240-88-2] (5.0 g, 43.8mmol) in CH₂Cl₂ (10 mL) was added TEA (12.3 mL, 87.7 mmol) followed bythe dropwise addition of methanesulfonyl chloride (5 mL, 65.8 mmol) at0° C. The resulting mixture was stirred at room temperature for 3 h. Thereaction mixture was diluted with CH₂C₂ and the organic phase was washedwith brine, dried over Na₂SO₄, filtered and concentrated to give thecrude product that was purified by silica gel chromatography elutingwith petroleum ether/ethyl acetate (30%) to give 3,3,3-trifluoropropylmethanesulfonate [911116-16-0] (46) (7.0 g, 83% yield) as light yellowoil. C₄H₇F₃O₃S: ¹H NMR (400 MHz, CDCl₃): 4.43 (t, J=5.6 Hz, 2H), 3.05(s, 3H), 2.66-2.55 (m, 2H).

Step-2:2-Amino-6-(benzyloxy)-9-(4-methoxybenzyl)-7-(3,3,3-trifluoropropyl)-7,9-dihydro-8H-purin-8-one(47)

To a stirred suspension of2-amino-6-(benzyloxy)-9-(4-methoxybenzyl)-7,9-dihydro-8H-purin-8-one (3)(8.0 g, 21.22 mmol), K₂CO₃ (5.85 g, 42.44 mmol) in DMF (100 mL) at 0° C.was added 3,3,3-trifluoropropyl methanesulfonate (46) (6.11 g, 31.83mmol). The reaction mixture was warmed to room temperature, stirred for16 h. and quenched with ice water (200 mL) and diethyl ether (80 mL) wasadded and stirred for 15 min. The resulting precipitate was collected byfiltration, washed with water and dried to afford2-amino-6-(benzyloxy)-9-(4-methoxybenzyl)-7-(3,3,3-trifluoropropyl)-7,9-dihydro-8H-purin-8-one(47) (6.5 g, 75%) as a brown solid; C₂₃H₂₂F₃N₅O₃: ¹H NMR (400 MHz,DMSO-d₆): 7.48 (d, J=6.8 Hz, 2H), 7.40 (d, J=6.8 Hz, 2H), 7.37 (m, 1H),7.20 (d, J=8.4 Hz, 2H), 6.87 (d, J=8.4 Hz, 2H), 6.46 (s, 2H), 5.42 (s,2H), 4.82 (s, 2H), 4.02 (t, J=6.8 Hz, 2H), 3.71 (s, 3H), 2.62 (m, 2H).ES+, m/z 474.1 [M+H]⁺.

Step-3:2-Amino-7-(3,3,3-trifluoropropyl)-7,9-dihydro-1H-purine-6,8-dione (48)

Trifluoromethane sulfonic acid (2.06 mL, 25.36 mmol) was added to asuspension of2-amino-6-(benzyloxy)-9-(4-methoxybenzyl)-7-(3,3,3-trifluoropropyl)-7,9-dihydro-8H-purin-8-one(47) (3.0 g, 6.3424 mmol) in trifluoroacetic acid (2.12 mL, 25.36 mmol)at room temperature under argon atmosphere and the resulting reactionmixture was stirred at room temperature for 8 h. The reaction mixturewas quenched with ice cold water. The pH of the reaction mixture wasmade basic with a sat. aq. NaHCO₃ solution under vigorous stirring andfiltered. The filtered solid was taken into ethyl acetate, stirred for30 min., filtered and dried to afford2-amino-7-(3,3,3-trifluoropropyl)-7,9-dihydro-1H-purine-6,8-dione (48)(1.2 g, 75%) as a brown solid. C₈H₈F₃N₅O₂: ¹H NMR (400 MHz, DMSO-d₆): δ11.17 (s, 1H), 10.74 (s, 1H), 6.41 (s, 2H), 3.97 (t, J=6.8 Hz, 2H),2.73-2.70 (m, 2H). ES+, m/z 264.1 [M+H]⁺.

Step-4:N-(6,8-Dioxo-7-(3,3,3-trifluoropropyl)-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide(49)

Acetic anhydride (0.69 mL, 6.844 mmol) was added to a solution of2-amino-7-(3,3,3-trifluoropropyl)-7,9-dihydro-1H-purine-6,8-dione (48)(1.2 g, 4.562 mmol) in AcOH (15 mL) at room temperature under an argonatmosphere and the resulting reaction mixture was stirred at 130° C. for8 h. The reaction mixture was cooled to 0° C., and the solids formedwere stirred for 30 minutes. The product was filtered, washed with EtOHand dried under vacuum to affordN-(6,8-dioxo-7-(3,3,3-trifluoropropyl)-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide(49) (800 mg, 61%) as a brown solid. C₁₀H₁₀F₃N₅O₃: ¹H NMR (400 MHz,DMSO-d₆): δ 12.05 (s, 1H), 11.77 (s, 1H), 11.68 (s, 1H), 4.06 (t, J=6.8Hz, 2H), 2.75 (m, 2H), 2.15 (s, 3H). ES+, m/z 306.1 [M+H]⁺.

Step-5:(S)-1-((2R,3S,4S,5R)-5-(2-Acetamido-6,8-dioxo-7-(3,3,3-trifluoropropyl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxy-3-fluorotetrahydrofuran-2-yl)propylacetate (50)

N-(6,8-dioxo-7-(3,3,3-trifluoropropyl)-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide(49) (350 mg, 1.147 mmol),(3S,4S,5R)-5-((S)-1-acetoxypropyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate (37S) (450 mg, 1.491 mmol) and BSA (0.873 mL, 3.441 mmol) weredissolved in 1,2-dichloroethane (20 mL) and the reaction mixture wasstirred at 80° C. for 30 min under argon. The reaction mixture wascooled to rt and 1,2-dichloroethane was removed by vacuum. The residuewas dissolved in MeCN (20 mL) followed by addition of TMSOTf (0.318 mL,1.720 mmol). The stirred reaction mixture was heated at 80° C. for 16 h,cooled to room temperature and concentrated under vacuum. To the residuewas added sat. aq. NaHCO₃ (60 mL) and then extracted with EtOAc (3×60mL). The combined EtOAc layers were washed with water (30 mL), brine (30mL), dried over Na₂SO₄, filtered and concentrated under vacuum. Thecrude compound was purified by flash column (80% EtOAc in pet ether) toafford(S)-1-((2R,3S,4S,5R)-5-(2-acetamido-6,8-dioxo-7-(3,3,3-trifluoropropyl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxy-3-fluorotetrahydrofuran-2-yl)propylacetate (50) (210 mg, 33%) as an off-white solid. C₂₁H₂₅F₄N₅O₈: ES+, m/z552.3 [M+H]⁺.

Step-6:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(3,3,3-trifluoropropyl)-7,9-dihydro-1H-purine-6,8-dione(Compound 27)

To a solution of(S)-1-((2R,3S,4S,5R)-5-(2-acetamido-6,8-dioxo-7-(3,3,3-trifluoropropyl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxy-3-fluorotetrahydrofuran-2-yl)propylacetate (50) (210 mg, 0.381 mmol) in methanol (6 mL) was added K₂CO₃ (79mg, 0.571 mmol) at room temperature. The reaction mixture was stirred atroom temperature for 16 h., and then concentrated under vacuum to afforda thick mass. The crude product was purified by GRACE reverse phasechromatography (0.1% HCO₂H:MeCN) to afford2-amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(3,3,3-trifluoropropyl)-7,9-dihydro-1H-purine-6,8-dione(Compound 27) (30 mg, 19%) as an off-white solid. C₁₅H₁₉F₄N₅O₅: ¹H NMRindicated the compound exist as the formic acid salt. ¹H NMR (500 MHz,DMSO-d₆): δ 11.25 (brs, 1H), 8.42 (s, 1H), 6.69 (s, 2H), 5.91 (s, 1H),5.39 (d, J=6.5 Hz, 1H), 5.32-5.25 (m, 1H), 4.98 (dt, J=48.5, 3.5 Hz,1H), 4.84 (d, J=6.0 Hz, 1H), 4.04 (t, J=7.0 Hz, 2H), 3.81 (dt, J=23.0,5.8 Hz, 1H), 3.52 (m, 1H), 2.75 (m, 2H), 1.49 (m, 1H), 1.34 (m, 1H),0.91 (t, J=7.5 Hz, 3H). ES+, m/z 426.2 [M+H]⁺.

Example 25:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-(3,3,3-trifluoropropyl)-7,9-dihydro-1H-purine-6,8-dione,Compound 28

Compound 28 was prepared according to the following two step procedure.

Step-1:(R)-1-((2S,4R,5R)-5-(2-Acetamido-6,8-dioxo-7-(3,3,3-trifluoropropyl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2,2,2-trifluoroethylacetate (51A) and(S)-1-((2S,4R,5R)-5-(2-Acetamido-6,8-dioxo-7-(3,3,3-trifluoropropyl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2,2,2-trifluoroethylacetate (51B)

To a suspension ofN-(6,8-dioxo-7-(3,3,3-trifluoropropyl)-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide(49) (500 mg, 1.63 mmol) and(2S,3R,5S)-5-(1-acetoxy-2,2,2-trifluoroethyl)tetrahydrofuran-2,3-diyldiacetate (22S) (645 mg, 1.96 mmol) in 1,2-dichloroethane (20 mL) wasadded BSA (1.24 mL, 4.91 mmol). The reaction mixture was stirred at 80°C. for 30 min under argon and then cooled to RT. The 1,2-dichloroethanewas removed under vacuum and the residue was dissolved in MeCN (20 mL)followed by addition of TMSOTf (0.44 mL, 2.45 mmol). The reactionmixture was heated at 80° C. for 16 h, cooled to room temperature andconcentrated under vacuum. To the concentrate was added sat. aq. NaHCO₃(50 mL) and extracted with EtOAc (3×50 mL). The combined EtOAc layerwere washed with water (30 mL), brine (30 mL), dried over anhydrousNa₂SO₄, filtered and concentrated under vacuum. The crude products werepurified by GRACE flash chromatography (80% EtOAc in pet. ether) toafford 350 mg (˜62:38 of a diastereomeric mixture by LC/MS) of(R,S)-1-((2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(3,3,3-trifluoropropyl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2,2,2-trifluoroethylacetate (51A:51B) as an off-white solid. Further purification byprep-HPLC (LUNA OMEGA C18(250*21.2), 5 u mobile phase: 10 mM ammoniumbicarbonate in H₂O:MeCN gradient: (T % B):—0/40, 8/65, 10/65, 10.1/98,14/98, 14.1/40, 17/40; Flow rate: 17 mL/min; Diluent: MeCN+H₂O+THF) gave60 mg of(R)-1-((2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(3,3,3-trifluoropropyl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2,2,2-trifluoroethylacetate (51A) and 40 mg of(S)-1-((2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(3,3,3-trifluoropropyl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2,2,2-trifluoroethylacetate (51A) both as off-white solids after lyophilization. (51A):C₂H₂₁F₆N₅O₈: ES+, m/z 574.4 [M+H]⁺. (51B): C₂H₂₁F₆N₅O₈: ES+, m/z 574.4[M+H]⁺.

Step-2:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-(3,3,3-trifluoropropyl)-7,9-dihydro-1H-purine-6,8-dione(Compound 28)

To a solution of(R)-1-((2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(3,3,3-trifluoropropyl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2,2,2-trifluoroethylacetate (51A) (60 mg, 0.1 mmol) in MeOH (20 mL) was added K₂CO₃ (21.6mg, 1.5 mmol) at 0° C. and the reaction mixture was stirred at RT for 16h. Methanol was removed under reduced pressure at 30° C. The residue wasdirectly purified by reverse phase GRACE flash chromatography (using 10mM ammonium bicarbonate in H₂O). The pure fractions were lyophilized toafford 25 mg (54%) of2-amino-9-((2R,3R,5S)-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-(3,3,3-trifluoropropyl)-7,9-dihydro-1H-purine-6,8-dione(Compound 28) as a white solid. C₁₄H₁₅F₆N₅O₅: ¹H NMR (400 MHz, DMSO-d₆):δ 11.07 (brs, 1H), 6.56 (brs, 2H), 6.31 (d, J=8.0 Hz, 1H), 5.58 (d,J=3.2 Hz, 1H), 5.53 (d, J=4.8 Hz, 1H), 4.73 (m, 1H), 4.33 (m, 1H), 4.05(t, J=6.8 Hz, 2H), 4.02 (m, 1H), 2.74 (m, 2H), 2.55 (m, 1H), 1.96 (m,1H). ES+, m/z 448.3 [M+H]⁺.

Example 26:2-Amino-7-(cyclopropylmethyl)-9-((2R,3R,5S)-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 29

Compound 29 was prepared according to the following two step procedure.

Step 1:(R)-1-((2S,4R,5R)-5-(2-Acetamido-7-(cyclopropylmethyl)-6,8-dioxo-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2,2,2-trifluoroethylacetate (52A) and(S)-1-((2S,4R,5R)-5-(2-Acetamido-7-(cyclopropylmethyl)-6,8-dioxo-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2,2,2-trifluoroethylacetate (52B)

2-Amino-7-(cyclopropylmethyl)-7,9-dihydro-1H-purine-6,8-dione (12) (350mg, 1.33 mmol),(2S,3R,5S)-5-(1-acetoxy-2,2,2-trifluoroethyl)tetrahydrofuran-2,3-diyldiacetate (22S) (567 mg, 1.73 mmol) and BSA (1.0 mL, 3.9 mmol) weredissolved in 1,2-dichloroethane (20 mL) and the mixture was stirred at80° C. for 30 min under argon. The reaction mixture was allowed to coolto rt and 1,2-dichloroethane was removed under vacuum. The residue wasdissolved in MeCN (20 mL) followed by the addition of TMSOTf (0.36 mL,1.99 mmol). The reaction mixture was heated at 80° C. for 16 h, cooledto room temperature and concentrated under vacuum. To the residueobtained was added sat. aq. NaHCO₃ (50 mL) and then extracted with EtOAc(3×50 mL). The combined EtOAc layer were washed with water (30 mL),brine (30 mL), dried over Na₂SO₄, filtered and concentrated undervacuum. The crude compound was purified by GRACE flash chromatography(using 80% EtOAc in pet ether as eluent) to afford 260 mg (˜5:3 mixtureof diastereomers) of(R,S)-1-((2S,4R,5R)-5-(2-acetamido-7-(cyclopropylmethyl)-6,8-dioxo-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2,2,2-trifluoroethylacetate (52A:52B) as an brown solid. Further purification by Prep-HPLC(LUNA OMEGA C18 (250*21.2), 5 u Mobile phase: 10 mM ammonium bicarbonatein H₂O:MeCN gradient: (T % B):—0/30, 8/60, 12/60, 12.1/98, 14/98,14.1/30, 17/30; Flow Rate: 17 mL/min; Diluent: MeCN+H₂O+THF) gave 130 mgof(R)-1-((2S,4R,5R)-5-(2-acetamido-7-(cyclopropylmethyl)-6,8-dioxo-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2,2,2-trifluoroethylacetate (52A) and 60 mg(S)-1-((2S,4R,5R)-5-(2-acetamido-7-(cyclopropylmethyl)-6,8-dioxo-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2,2,2-trifluoroethyl acetate (52B), both asoff-white solids after lyophilization. (52A): C₂₁H₂₄F₃N₅O₈: ES+, m/z532.4 [M+H]⁺. (52B): C₂₁H₂₄F₃N₅O₈: ES+, m/z 532.4 [M+H]⁺.

Step 2:2-Amino-7-(cyclopropylmethyl)-9-((2R,3R,5S)-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7,9-dihydro-1H-purine-6,8-dione(Compound 29)

To a solution of(R)-1-((2S,4R,5R)-5-(2-acetamido-7-(cyclopropylmethyl)-6,8-dioxo-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2,2,2-trifluoroethylacetate(52A) (130 mg, 0.24 mmol) in MeOH (20 mL) was added K₂CO₃ (50.6 mg, 0.36mmol) at 0° C. The reaction mixture was stirred at rt for 16 h whereuponmethanol was removed under reduced pressure at 30° C. The residue waspurified by reverse phase GRACE flash chromatography (using 0.01% aq.NH₄HCO₃ and MeCN). The pure fractions were lyophilized to afforded 75 mg(75%) of2-amino-7-(cyclopropylmethyl)-9-((2R,3R,5S)-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7,9-dihydro-1H-purine-6,8-dione(Compound 29) as a white solid. C₁₅H₁₈F₃N₅O₅: ¹H NMR (400 MHz, DMSO-d₆):δ 10.95 (brs, 1H), 6.50 (brs, 2H), 6.33 (d, J=8.4 Hz, 1H), 5.59 (d,J=3.6 Hz, 1H), 5.53 (d, J=4.8 Hz, 1H), 4.77 (m, 1H), 4.34 (m, 1H), 4.03(m, 1H), 3.65 (d, J=7.2 Hz, 2H), 2.54 (m, 1H), 1.97 (m, 1H), 1.18 (m,1H), 0.41 (m, 2H), 0.35 (m, 2H). ES+, m/z 406.0 [M+H]⁺.

Example27:2-Amino-7-butyl-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 30

Compound 30 was prepared according to the following multi-stepprocedure.

Step 1:2-Amino-6-(benzyloxy)-7-butyl-9-(4-methoxybenzyl)-7,9-dihydro-8H-purin-8-one(53)

Butyl bromide (2.15 mL, 15.9 mmol) was added to a suspension of2-amino-6-(benzyloxy)-9-(4-methoxybenzyl)-7,9-dihydro-8H-purin-8-one (3)(5 g, 13.25 mmol), K₂CO₃ (2.7 g, 19.85 mmol) in DMF (80 mL) at 0° C. andstirred at room temperature for 18 h. The reaction mixture was quenchedwith ice water (120 mL), diluted with diethyl ether (80 mL) and stirredfor 15 min. The resulting precipitated solid was collected byfiltration, washed with water and dried to afford2-amino-6-(benzyloxy)-7-butyl-9-(4-methoxybenzyl)-7,9-dihydro-8H-purin-8-one(53) (4.9 g, 85%) as a brown solid. C₂₄H₂₇N₅O₃: ¹H NMR (400 MHz,DMSO-d₆): δ 7.47 (d, J=6.8 Hz, 2H), 7.40 (d, J=6.8 Hz, 2H), 7.37 (m,1H), 7.20 (d, J=8.4 Hz, 2H), 6.87 (d, J=8.8 Hz, 2H), 6.39 (s, 2H), 5.41(s, 2H), 4.82 (s, 2H), 3.74 (m, 2H), 3.71 (s, 3H), 1.53 (m, 2H), 1.15(m, 2H), 0.77 (t, J=7.4 Hz, 3H). ES+, m/z 434.1 [M+H]⁺.

Step 2: 2-Amino-7-butyl-7,9-dihydro-1H-purine-6,8-dione (54)

Trifluoromethanesulfonic acid (2.99 mL, 33.9 mmol) was added to asuspension of2-amino-6-(benzyloxy)-7-butyl-9-(4-methoxybenzyl)-7,9-dihydro-8H-purin-8-one(53) (4.9 g, 11.31 mmol) in triflouroacetic acid (2.59 mL, 33.9 mmol) at0° C. under argon atmosphere. The reaction mixture was slowly warmed toroom temperature and stirred for 3 h. To the reaction mixture was addedice cold water and pH was made basic with a sat. aq. NaHCO₃ solutionwhile being stirred vigorously. The resultant solids were filtered offand taken up in ethyl acetate (50 mL), stirred for 30 min. filtered anddried to afford 2-amino-7-butyl-7,9-dihydro-1H-purine-6,8-dione (54)(2.0 g, 79%) as a brown solid. C₉H₁₃N₅O₂: ¹H NMR (400 MHz, DMSO-d₆): δ11.05 (s, 1H), 10.62 (s, 1H), 6.33 (s, 2H), 3.71 (t, J=7.0 Hz, 2H), 1.57(m, 2H), 1.23 (m, 2H), 0.8 (t, J=7.4 Hz, 3H). ES+, m/z 224.1 [M+H]⁺.

Step 3: N-(7-Butyl-6,8-dioxo-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide(55)

Acetic anhydride (2.54 ml, 26.90 mmol) was added to a solution of2-amino-7-butyl-7,9-dihydro-1H-purine-6,8-dione (54) (2 g, 8.96 mmol) inAcOH (20 mL) at ambient temperature under argon atmosphere. The reactionmixture was stirred at 130° C. for 3 h under argon, cooled down to 0° C.Solids formed and stirring was continued for 30 minutes. The product wasfiltered, washed with ethanol and dried under vacuum to affordN-(7-butyl-6,8-dioxo-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide (55)(1.5 g, 66%) as a brown solid. C₁₁H₁₃N₅O₃: ES+, m/z 266.3 [M+H]⁺.

Step 4:(S)-1-((2R,3S,4S,5R)-5-(2-Acetamido-7-butyl-6,8-dioxo-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxy-3-fluorotetrahydrofuran-2-yl)propylacetate (56)

To N-(7-butyl-6,8-dioxo-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide (55)(340 mg, 1.28 mmol), and(3S,4S,5R)-5-((S)-1-acetoxypropyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate (37S) (504 mg, 1.66 mmol) in 1,2-dichloroethane (10 mL) wasadded BSA (777 mg, 3.84 mmol). The reaction mixture was stirred at 80°C. for 30 min under argon, cooled to RT and 1,2-dichloroethane wasremoved under vacuum. The residue was dissolved in MeCN (20 mL) andTMSOTf (0.43 mL, 1.92 mmol) was added. The reaction mixture was heatedat 80° C. for 16 h, cooled to room temperature and concentrated undervacuum. To the residue was added sat. aq. NaHCO₃ (50 mL) and thenextracted with EtOAc (3×50 mL). The combined EtOAc layer were washedwith water (30 mL), brine (30 mL), dried over Na₂SO₄, filtered andconcentrated under vacuum. The crude product was purified by GRACE flashchromatography (using 80% EtOAc in pet ether) to afford (150 mg, 22.9%)of(S)-1-((2R,3S,4S,5R)-5-(2-acetamido-7-butyl-6,8-dioxo-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxy-3-fluorotetrahydrofuran-2-yl)propylacetate (56) as an yellow gummy solid. C₂₂H₃₀FN₅O₈: ES+, m/z 512.4[M+H]⁺.

Step 5:2-Amino-7-butyl-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7,9-dihydro-1H-purine-6,8-dione,(Compound 30)

To a solution of(S)-1-((2R,3S,4S,5R)-5-(2-acetamido-7-butyl-6,8-dioxo-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxy-3-fluorotetrahydrofuran-2-yl)propylacetate (56) (150 mg, 0.29 mmol) in MeOH (10 mL) was added K₂CO₃ (60 mg,0.44 mmol) at 0° C. and the reaction mixture was stirred at RT for 16 h.Methanol was removed under reduced pressure at 30° C. The residue wasadded directly to normal phase GRACE flash chromatography (using 7% MeOHin CH₂Cl₂) followed by reverse phase GRACE flash chromatography (using0.01% aq. HCO₂H in MeCN). The pure fractions were collected andlyophilized to afford (20 mg, 17.69%) of2-amino-7-butyl-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7,9-dihydro-1H-purine-6,8-dione(Compound 30) as a white solid. C₁₆H₂₄FN₅O₅: ¹H NMR (500 MHz, DMSO-d₆):δ 10.90 (s, 1H), 6.51 (brs, 2H), 5.90 (d, J=5.5 Hz, 1H), 5.37-5.32 (m,2H), 5.00 (dt, J=55.5, 2.5 Hz, 1H), 4.84 (d, J=7.0 Hz, 1H), 3.83 (m,1H), 3.78 (t, J=3.5 Hz, 2H), 3.51 (m, 1H), 1.60 (m, 2H), 1.51 (m, 1H),1.33 (m, 1H), 1.26 (m, 2H), 0.91 (t, J=7.5 Hz, 3H), 0.88 (t, J=7.5 Hz,3H). ES+, m/z 386.2 [M+H]⁺.

Example 28:2-Amino-7-butyl-9-((2R,3R,5S)-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 31

Compound 31 was prepared according to the following two step procedure.

Step 1:(R)-1-((2S,4R,5R)-5-(2-Acetamido-7-butyl-6,8-dioxo-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2,2,2-trifluoroethylacetate (57A) and(S)-1-((2S,4R,5R)-5-(2-Acetamido-7-butyl-6,8-dioxo-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2,2,2-trifluoroethylacetate (57B)

N-(7-Butyl-6,8-dioxo-6,7,8,9-tetrahydro-1H-purin-2-yl) acetamide (55)(350 mg, 1.32 mmol),(2S,3R,5S)-5-(1-acetoxy-2,2,2-trifluoroethyl)tetrahydrofuran-2,3-diyldiacetate (22S) (563 mg, 1.71 mmol) and BSA (1 mL, 3.9 mmol) weredissolved in 1,2-dichloroethane (20 mL) and the resulting reactionmixture was stirred at 80° C. for 30 min under argon. The reactionmixture was allowed to cool to rt and 1,2-dichloroethane was removedunder vacuum. The residue was dissolved in MeCN (20 mL) followed byaddition of TMSOTf (0.36 mL, 1.98 mmol), and the reaction mixture washeated at 80° C. for 16 h. At this time the reaction mixture was cooledto room temperature and concentrated under vacuum. A saturated.aq·NaHCO₃ (50 mL) solution was added to the residue and extracted withEtOAc (3×50 mL). The combined EtOAc layer was washed with water (30 mL),brine (30 mL), dried over Na₂SO₄, filtered and concentrated undervacuum. The crude compound was purified by GRACE flash chromatography(80% EtOAc in pet ether) to afford 250 mg (46% and 29% of adiastereomeric mixture by LC/MS) of(R,S)-1-((2S,4R,5R)-5-(2-acetamido-7-butyl-6,8-dioxo-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2,2,2-trifluoroethylacetate as an brown solid. Further purification by Prep-HPLC(X-SELECT-C18 (250*19 MM), 5 u Mobile phase: 10 mM ammonium bicarbonatein H₂O:MeCN gradient: (T % B):—0/30, 8/5, 13/55, 13.1/98, 15/98,15.1/30, 18/3; Flow Rate: 7 mL/min; Diluent: MeCN+H₂O+THF) gave 90 mg of(R)-1-((2S,4R,5R)-5-(2-acetamido-7-butyl-6,8-dioxo-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2,2,2-trifluoroethylacetate (57A) (peak-1) and 60 mg(S)-1-((2S,4R,5R)-5-(2-acetamido-7-butyl-6,8-dioxo-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2,2,2-trifluoroethylacetate (57B) (peak-2), both as off-white solids after lyophilization ofthe pure fractions collected. (57A): C₂₁H₂₆F₃N₅O₈: ¹H NMR (500 MHz,DMSO-d₆): δ 12.15 (bs, 1H), 11.61 (brs, 1H), 5.75 (s, 1H), 5.65 (m, 2H),4.53 (m, 1H), 3.86 (t, J=6.8 Hz, 2H), 2.83 (bs, 1H), 2.17 (s, 3H), 2.14(m, 1H), 2.08 (s, 6H), 1.64 (m, 2H), 1.27 (m, 2H), 0.87 (t, J=7.3 Hz,3H). ES+, m/z 534.0 [M+H]⁺. (57B): C₂₁H₂₆F₃N₅O₈: ¹H NMR (500 MHz,CDCl₃): δ 12.10 (bs, 1H), 9.47 (brs, 1H), 6.19 (s, 1H), 6.04 (m, 1H),5.38 (d, J=6.0 Hz, 1H), 4.66 (m, 1H), 4.00 (t, J=7.3 Hz, 2H), 2.93 (m,1H), 2.30 (s, 3H), 2.26 (s, 3H), 2.17 (m, 1H), 2.12 (s, 3H), 1.74 (m,2H), 1.37 (m, 2H), 0.94 (t, J=7.3 Hz, 3H). ES+, m/z 534.4 [M+H]⁺.

Step 2:2-Amino-7-butyl-9-((2R,3R,5S)-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7,9-dihydro-1H-purine-6,8-dione,(Compound 31)

To a solution of(R)-1-((2S,4R,5R)-5-(2-acetamido-7-butyl-6,8-dioxo-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2,2,2-trifluoroethylacetate (57A) (90 mg, 0.16 mmol) in MeOH (20 mL) was added K₂CO₃ (34.9mg, 0.25 mmol) at 0° C. The reaction mixture was stirred at rt for 16 h.and methanol was removed under reduced pressure at 30° C. The residuewas subjected directly to reverse phase GRACE flash chromatography(using 10 mM ammonium bicarbonate in H₂O). The pure fractions onlyophilization afforded 50 mg (73%) of2-amino-7-butyl-9-((2R,3R,5S)-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7,9-dihydro-1H-purine-6,8-dione(Compound 31) as an off-white solid. C₁₅H₂₀F₃N₅O₅: ¹H NMR (500 MHz,DMSO-d₆): δ 11.00 (brs, 1H), 6.51 (brs, 2H), 6.35 (d, J=8.5 Hz, 1H),5.58 (d, J=3.5 Hz, 1H), 5.52 (d, J=5.0 Hz, 1H), 4.74 (m, 1H), 4.34 (dt,J=11.3, 3.6 Hz, 1H), 4.02 (m, 1H), 3.78 (t, J=7.0 Hz, 2H), 2.51 (m, 1H),1.97 (m, 1H), 1.60 (m, 2H), 1.24 (m, 2H), 0.88 (t, J=7.5 Hz, 3H). ES+,m/z 408.3 [M+H]⁺.

Example 29:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(2-hydroxyethyl)-7,9-dihydro-1H-purine-6,8-dione,Compound 32

Compound 32 was prepared according to the following multi-stepprocedure.

Step 1:2-Amino-6-(benzyloxy)-7-(2-hydroxyethyl)-9-(4-methoxybenzyl)-7,9-dihydro-8H-purin-8-one(58)

2-Bromoethan-1-ol (2.4 mL, 33.1 mmol) was added to a suspension of2-amino-6-(benzyloxy)-9-(4-methoxybenzyl)-7,9-dihydro-8H-purin-8-one (3)(5.0 g, 13.2 mmol), Cs₂CO₃ (5.4 g, 39.8 mmol) in DMF (50 mL) at 0° C.After the reaction mixture was stirred at 80° C. for 72 h. ice water(100 mL) was added and stirring was continued for 1 h. The resultingprecipitated solid was filtered, washed with water, EtOAc and dried toafford 4 g of2-amino-6-(benzyloxy)-7-(2-hydroxyethyl)-9-(4-methoxybenzyl)-7,9-dihydro-8H-purin-8-one(58) as an off white solid contaminated with 10% starting purine (3) byLC/MS and ¹H NMR. C₂₂H₂₃N₅O₄: ES+, m/z 422.0 [M+H]⁺ and C₂₀H₁₉N₅O: 378.0[M+H]⁺. ¹H NMR (400 MHz, DMSO-d₆): δ 10.80 (s, N^(7H)(4)), 7.49-7.18 (m,9H), 6.87 (dd, J=8.4, 1.2 Hz, 2H), 6.36 (s, 1H), 6.39 (s, 1H), 5.42 (d,J=7.2 Hz, 2H), 4.81 (d, J=15.6 Hz, 2H), 4.76 (m, 1H), 3.84 (t, J=6.2 Hz,1H), 3.71 (s, 3H), 3.57 (q, J=6.0 Hz, 1H).

Step 2: 2-Amino-7-(2-hydroxyethyl)-7,9-dihydro-1H-purine-6,8-dione (59)

Trifluoromethane sulfonic acid (5.0 mL, 57.0 mmol) was added to asuspension2-amino-6-(benzyloxy)-7-(2-hydroxyethyl)-9-(4-methoxybenzyl)-7,9-dihydro-8H-purin-8-one(58) (4.0 g, 9.5 mmol) in trifluoroacetic acid (4.6 mL, 57.0 mmol) at 0°C. under argon atmosphere. The reaction mixture was slowly warmed toroom temperature and stirred for 16 h. whereupon ice cold water wasadded. With vigorous stirring the pH of the mixture was made basic withconc. aq. NH₃. The solids formed were filtered and taken up in ethylacetate, stirred for 30 min., filtered and dried to afford 1.8 g of2-amino-6-hydroxy-7-(2-hydroxyethyl)-7,9-dihydro-8H-purin-8-one (59) asa brown solid. C₇H₉N₅O₃: ES+, m/z 212.0 [M+H]⁺. ¹H NMR (500 MHz,DMSO-d₆): δ 10.82 (s, 1H), 10.53 (s, 1H), 6.29 (s, 2H), 4.75 (t, J=5.8Hz, 1H), 3.78 (t, J=6.0 Hz, 2H), 3.57 (m, 2H).

Step 3: 2-(2-Acetamido-6,8-dioxo-1,6,8,9-tetrahydro-7H-purin-7-yl)ethylacetate (60)

Acetic anhydride (3.3 mL, 34.1 mmol) was added to a solution of2-amino-6-hydroxy-7-(2-hydroxyethyl)-7,9-dihydro-8H-purin-8-one (59)(1.8 g, 8.53 mmol) in AcOH (20 mL) at room temperature and the reactionmixture was heated at 120° C. for 16 h under an argon atmosphere. Thereaction mixture was cooled to 0° C. and stirred for 30 minutes. Thesolids that precipitated were filtered, washed with EtOAc and driedunder vacuum to afford 1.3 g of2-(2-acetamido-6-hydroxy-8-oxo-8,9-dihydro-7H-purin-7-yl)ethyl acetate(60) as an brown solid. C₁₁H₁₃N₅O₅: ES+, m/z 296.0 [M+H]⁺. Th crudeproduct was used directly in the next step without purification.

Step 4:(S)-1-((2S,4R,5R)-5-(2-Acetamido-7-(2-acetoxyethyl)-6,8-dioxo-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)propylacetate (61)

2-(2-Acetamido-6-hydroxy-8-oxo-8,9-dihydro-7H-purin-7-yl)ethylacetate(60) (1.0 g. 3.3 mmol),(3R,5S)-5-((S)-1-acetoxypropyl)tetrahydrofuran-2,3-diyl diacetate (14S)(1.17 g, 4.06 mmol) and BSA (2.5 mL, 10.1 mmol) were dissolved in1,2-dichloroethane (20 mL). The reaction mixture was stirred at 800° C.for 30 min under argon and concentrated under reduced pressure. To theremaining residue was added MeCN (20 mL) and to this solution was addedTMSOTf (0.94 mL, 5.08 mmol). The reaction mixture was placed into apre-heated oil bath at 80° C., stirred for 16 h and then cooled to roomtemperature. The solvent was removed under reduced pressure and solidswere dissolved in ethyl acetate (100 mL) and washed with saturatedaqueous NaHCO₃ (1×30 mL). The organic phase was dried over Na₂SO₄,filtered and concentrated. The crude compound was purified by columnchromatography (SiO₂, 0 to 60% EtOAc-Pet-ether) to afford 250 mg (13%)of(S)-1-((2S,4R,5R)-5-(2-acetamido-7-(2-acetoxyethyl)-6,8-dioxo-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)propylacetate (61) as a pale yellow solid. C₂₂H₂₉N₅O₁₀: ES+, m/z 523.9 [M+H]⁺.

Step 5:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(2-hydroxyethyl)-7,9-dihydro-1H-purine-6,8-dione,(Compound 32)

To a solution of(S)-1-((2S,4R,5R)-5-(2-acetamido-7-(2-acetoxyethyl)-6,8-dioxo-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)propylacetate (61) (250 mg, 0.47 mmol) in methanol (15 mL) at room temperaturewas added K₂CO₃ (98.9 mg, 0.71 mmol). The reaction mixture was stirredat room temperature for 16 h. After complete consumption of the startingmaterial as indicated by LC/MS, the reaction mixture was concentratedunder reduced pressure. The crude product was purified by Prep-HPLCusing Column: LUNA OMEGA C18 (250*21.2), 5 u Mobile phase: 10 mM NH₄HCO₃in H₂O:MeOH gradient: (T % B):—0/10, 8/50, 12/60, 12.1/98, 14/98, 14/10,18/10; Flow Rate: 16 mL/min; Diluent: MeCN+H₂O+THF. Lyophilization ofthe pure fractions afforded 20 mg of2-amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(2-hydroxyethyl)-7,9-dihydro-1H-purine-6,8-dione(Compound 32) as an off-white solid: C₁₄H₂₁N₅O₆: ¹H NMR (400 MHz,DMSO-d₆): δ 11.10 (brs, 1H), 6.51 (s, 2H), 5.52 (d, J 3.2 Hz, 1H), 5.34(d, J 4.8 Hz, 1H), 4.87 (brs, 1H), 4.75 (m, 1H), 4.63 (d, J=6.8 Hz, 1H),4.01 (m, 1H), 3.83 (t, J=6.0 Hz, 2H), 3.59 (m, 2H), 3.27 (m, 1H), 2.38(m, 1H), 1.77 (m, 1H), 1.39 (m, 1H), 1.28 (m, 1H), 0.87 (t, J 7.2 Hz,3H). ES+, m/z 356.0 [M+H]⁺.

Example 30: Compound 33 and 342-Amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-((R)-2-hydroxypropyl)-7,9-dihydro-1H-purine-6,8-dione,Compound 33

2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-((S)-2-hydroxypropyl)-7,9-dihydro-1H-purine-6,8-dione,Compound 34

Compounds 33 and 34 were prepared according to the following multi-stepprocedures.

Step 1:2-Amino-6-(benzyloxy)-7-(2-hydroxypropyl)-9-(4-methoxybenzyl)-7,9-dihydro-8H-purin-8-one(62)

To a stirred suspension of2-amino-6-(benzyloxy)-9-(4-methoxybenzyl)-7,9-dihydro-8H-purin-8-one (3)(5 g, 13.26 mmol), K₂CO₃ (2.74 g, 19.89 mmol) in DMF (50 mL) at 0° C.was added 1-bromopropan-2-ol (2.765 g, 19.89 mmol). Stirring wascontinued at 90° C. for 48 h. To the stirred reaction mixture was addedice water (500 mL) followed by diethyl ether (80 mL). After about 15min. the resulting precipitated solid was filtered, washed with waterand dried to afford2-amino-6-(benzyloxy)-7-(2-hydroxypropyl)-9-(4-methoxybenzyl)-7,9-dihydro-8H-purin-8-one(62) (2 g, 34.66%) as an off-white solid. C₂₃H₂₅N₅O₄: ¹H NMR (400 MHz,DMSO-d₆): δ 7.48 (d, J=7.2 Hz, 2H), 7.41-7.32 (m, 3H), 7.21 (d, J=8.8Hz, 2H), 6.87 (d, J=8.4 Hz, 2H), 6.36 (s, 2H), 5.41 (q, J=12.4 Hz, 2H),4.82 (s, 2H), 4.74 (s, 1H), 3.90 (m, 1H), 3.77 (m, 1H), 3.71 (s, 3H),3.57 (dd, J=13.6, 5.2 Hz, 1H), 0.941 (d, J=6.4 Hz, 3H). ES+, m/z 436.4[M+H]⁺.

Step 2: 2-Amino-7-(2-hydroxypropyl)-7,9-dihydro-1H-purine-6,8-dione (63)

Trifluoromethanesulfonic acid (1.55 mL, 10.34 mmol) was added to asuspension of2-amino-6-(benzyloxy)-7-(2-hydroxypropyl)-9-(4-methoxybenzyl)-7,9-dihydro-8H-purin-8-one(62) (1.5 g, 3.44 mmol) in trifluoroacetic acid (1.18 mL, 10.34 mmol) at0° C. under argon atmosphere with stirring. The reaction mixture wasslowly warmed to room temperature and stirred for 16 h. The crudeproduct was purified by reverse phase GRACE flash chromatography using0.1% of HCO₂H in water and MeCN to afford2-amino-7-(2-hydroxypropyl)-7,9-dihydro-1H-purine-6,8-dione (63) (0.4 g,47.4%) as an off-white solid. C₈H₁₁N₅O₃: ¹H NMR (400 MHz, DMSO-d₆): δ11.08 (s, 1H), 10.69 (s, 1H), 6.35 (s, 2H), 4.8 (bs, 1H), 3.94 (m, 1H),3.69 (dd, J=13.4, 6.6 Hz, 1H), 3.59 (dd, J=13.6, 6.0 Hz, 1H), 0.99 (d,J=5.6 Hz, 3H). ES+, m/z 226.0 [M+H]⁺.

Step 3:I-(2-Acetamido-6,8-dioxo-1,6,8,9-tetrahydro-7H-purin-7-yl)propan-2-ylacetate (64)

Acetic anhydride (0.79 mL, 7.73 mmol) was added to a solution of2-amino-7-(2-hydroxypropyl)-7,9-dihydro-1H-purine-6,8-dione (63) (0.58g, 2.57 mmol) in AcOH (10 mL) at ambient temperature under argonatmosphere and the resulting reaction mixture was stirred at 120° C. for8 h under argon atmosphere. The reaction mixture was concentrated, EtOAc(20 mL) was added and stirring was continued for 30 minutes. The productwas filtered, washed with EtOAc and dried under vacuum to afford1-(2-acetamido-6,8-dioxo-1,6,8,9-tetrahydro-7H-purin-7-yl)propan-2-ylacetate (64) (500 mg, 62.81%) as a light brown solid. C₁₂H₁₅N₅O₅: ¹H NMR(400 MHz, DMSO-d₆): δ 12.00 (s, 1H), 11.70 (s, 1H), 11.66 (s, 1H), 5.15(m, 1H), 3.97 (dd, J=14.2, 7.4 Hz, 1H), 3.90 (dd, J=14.0, 4.4 Hz, 1H),2.15 (s, 3H), 1.88 (s, 3H), 1.17 (d, J=6.4 Hz, 3H). ES+, m/z 310.0[M+H]⁺.

Step 4:(S)-1-((2S,4R,5R)-5-(2-acetamido-7-((R)-2-acetoxypropyl)-6,8-dioxo-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)propylacetate (65A) and(S)-1-((2S,4R,5R)-5-(2-acetamido-7-((S)-2-acetoxypropyl)-6,8-dioxo-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)propylacetate (65B)

1-(2-Acetamido-6,8-dioxo-1,6,8,9-tetrahydro-7H-purin-7-yl)propan-2-ylacetate (64) (400 mg, 1.29 mmol),(3R,5S)-5-((S)-1-acetoxypropyl)tetrahydrofuran-2,3-diyl diacetate (14S)(559 mg, 1.94 mmol) and BSA (1.30 mL, 6.47 mmol) were dissolved in1,2-dichloromethane (15 mL). The reaction mixture was stirred at 80° C.for 30 min. under argon. At this time the reaction mixture wasconcentrated under reduced pressure, and the residue was dissolved inMeCN (30 mL) followed by addition of TMSOTf (0.71 mL, 3.2 mmol). Thestirred reaction mixture was placed into a pre-heated oil bath at 80° C.After 3 h the reaction mixture was cooled to room temperature and thesolvent was removed under reduced pressure. The resultant solid wasdissolved in ethyl acetate (80 mL) and to the stirred solution was addedsaturated aqueous NaHCO₃ (2×30 mL). The organic phase was separated,dried over anhydrous Na₂SO₄, filtered and concentrated. The crudeproducts was purified by column chromatography (SiO₂, 0 to 80% ethylacetate-pet ether) to give a 1:1 mixture of(S)-1-((2S,4R,5R)-5-(2-acetamido-7-((R,S)-2-acetoxypropyl)-6,8-dioxo-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)propylacetate (220 mgs). The racemic mixture was further purified by ChiralSFC-150-080 HPLC (Lux; Cellulose-4 OX-H; 250×30×5μ; 75% CO₂, 25% MeOH;Total Flow: 60.0 g/min.; Back pressure: 120.0 bar; 30° C.; UV: 214.0 nm;Stack time: 7.0 mins; Load/injection: 14.57 mgs) to afford 50 mg of(S)-1-((2S,4R,5R)-5-(2-acetamido-7-((R)-2-acetoxypropyl)-6,8-dioxo-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)propylacetate (65A; 7(R) stereochemistry arbitrarily assigned) and 50 mg of(S)-1-((2S,4R,5R)-5-(2-acetamido-7-((S)-2-acetoxypropyl)-6,8-dioxo-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)propylacetate (65B; 7(S) stereochemistry arbitrarily assigned), both asoff-white solids after evaporation of methanol. Analytical SFC was usedto check diastereomeric purity; (Chiralcel OX-H; 250×4.6×5μ; 75% CO₂,25% MeOH; Total Flow: 3.0 g/min.; Back pressure: 100.0 bar; 30° C.; UV:214.0 nm) 65A: C₂₃H₃₁N₅O₁₀: ES+, m/z 538.0 [M+H]⁺. 65B: C₂₃H₃₁N₅O₁₀:ES+, m/z 537.9 [M+H]⁺.

Step 5:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-((R)-2-hydroxypropyl)-7,9-dihydro-1H-purine-6,8-dione(Compound 33)

To a solution of(S)-1-((2S,4R,5R)-5-(2-acetamido-7-((R)-2-acetoxypropyl)-6,8-dioxo-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)propylacetate (65A) (50 mg, 0.09 mmol) in methanol (5 mL) at room temperature,was added K₂CO₃ (19 mg, 0.13 mmol) and the reaction mixture was stirredat room temperature for 16 h. At this time the solvent was removed underreduced pressure and the resulting crude compound was purified by GRACEflash chromatography (0.1% HCO₂H in water, acetonitrile) to afford2-amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-((R)-2-hydroxypropyl)-7,9-dihydro-1H-purine-6,8-dione(Compound 33) (24 mg, 69.66%), as a yellow solid. C₁₅H₂₃N₅O₆: ¹H NMRindicated formation of the formic acid salt. ¹H NMR (500 MHz, DMSO-d₆):δ 8.52 (s, 1H), 6.70-6.50 (b, 2H), 5.52 (d, J=3.5 Hz, 1H), 5.35 (s, 1H),4.75 (s, 2H), 4.01 (m, 1H), 3.91 (m, 1H), 3.70 (m, 2H), 3.20 (m, 1H),2.38 (m, 2H), 1.79 (m, 1H), 1.39 (m, 1H), 1.28 (m, 1H), 1.01 (d, J=6.5Hz, 3H), 0.87 (t, J=7.5 Hz 3H). ES+, m/z 370.36 [M+H]⁺.

Step 6:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-((S)-2-hydroxypropyl)-7,9-dihydro-1H-purine-6,8-dione(Compound 34)

To a solution of(S)-1-((2S,4R,5R)-5-(2-acetamido-7-((S)-2-acetoxypropyl)-6,8-dioxo-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)propylacetate (65B) (50 mg, 0.093 mmol) in methanol (5 mL) at room temperaturewas added K₂CO₃ (19 mg, 0.13 mmol). After stirring the reaction mixtureat room temperature for 16 h. the solvent was removed under reducedpressure. The resulting crude product was purified by GRACE flashchromatography (0.1% HCO₂H in water, acetonitrile) to afford2-amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-((S)-2-hydroxypropyl)-7,9-dihydro-1H-purine-6,8-dione(Compound 34) (15 mg, 43.54%), as a white solid. C₁₅H₂₃N₅O₆: ¹H NMR (400MHz, DMSO-d₆): δ 11.15 (s, 1H), 6.54 (s, 2H), 5.52 (d, J=3.2 Hz, 1H),5.34 (s, 1H), 4.85 (bs, 1H), 4.75 (s, 1H), 4.57 (d, J=6.4 Hz, 1H),4.03-3.92 (m, 2H), 3.75 (dd, J=13.6, 6.8 Hz, 1H), 3.64 (dd, J=13.4, 5.8Hz, 1H), 3.26 (m, 1H), 2.38 (m, 1H), 1.77 (m, 1H), 1.39 (m, 1H), 1.28(m, 1H), 1.01 (d, J=6.0 Hz, 3H), 0.89 (t, J=7.5 Hz, 3H). ES+, m/z 370.0[M+H]⁺.

Example31:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxybut-3-yn-1-yl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 35

Compound 35 was prepared according to the following multi-stepprocedure.

Step 1:(R)-1-((3aR,5S,6aR)-2,2-Dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)but-3-yn-1-ol(68S)

To a solution of(3aR,5S,6aR)-2,2-dimethyl-5-((R)-oxiran-2-yl)tetrahydrofuro[2,3-d][1,3]dioxole(9S) (4 g, 21.7 mmol) in DMSO (50 mL), was added lithiumacetylide-ethylenediamine complex (4.9 g, 53.76 mmol) at rt. Thereaction was monitored by TLC and the mixture was stirred for 18 hr. Thereaction mixture was poured into 100 mL of ice-water and extracted withdiethyl ether (2×100 mL). The organic phase was washed with a brinesolution (2×100 mL), separated and dried over Na₂SO₄, filtered andconcentrated to give the crude product that was purified by silica gelchromatography using a petroleum ether/ethyl acetate gradient (0-30%),to give(R)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)but-3-yn-1-ol(68S) (2.5 g, 55%) as an orange liquid. C₁₁H₁₆O₄: ¹H NMR (400 MHz,CDCl₃): δ 5.81 (d, J=3.6 Hz, 1H), 4.76 (t, J=4.4 Hz, 1H), 4.31 (dt,J=10.6, 4.4 Hz, 1H), 4.00 (ddd, J=10.4, 6.6, 3.8 Hz, 1H), 2.49-2.37 (m,2H), 2.30 (d, J=6.5 Hz, 1H), 2.09 (dd, J=13.5, 4.6 Hz, 1H), 2.05 (t,J=2.6 Hz, 1H), 1.86 (ddd, J=13.4, 10.6, 4.8 Hz, 1H), 1.52 (s, 3H), 1.35(s, 3H).

Step 2:(S)-1-((3aR,5S,6aR)-2,2-Dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)but-3-yn-1-yl4-nitrobenzoate (69S)

To a solution of(R)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)but-3-yn-1-ol(68S) (2.5 g, 11.7 mmol) in THE (60 mL) was added 4-nitrobenzoic acid(3.9 g, 23.5 mmol), triphenyl phosphine (3.0 g, 23.5 mmol) and DEAD (3.7mL, 23.5 mmol) at 0° C. The reaction mixture was monitored by TLC andstirring was continued for 16 hours at rt. At this time the reactionmixture was poured into 200 mL of water and extracted with EtOAc (2×200mL). The organic phase was washed with a sat. brine solution (2×60 mL),separated, dried over anhydrous Na₂SO₄, filtered and concentrated toafford the crude product that was purified by column chromatography withsilica and a petroleum ether/ethyl acetate gradient (0-20%) to yield(S)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)but-3-yn-1-yl4-nitrobenzoate (69S) (2.5 g, 59%) as a semi-solid. C₁₈H₁₉NO₇:

Step 3:(S)-1-((3aR,5S,6aR)-2,2-Dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)but-3-yn-1-ol(70S)

To a solution of(S)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)but-3-yn-1-yl4-nitrobenzoate (69S) (2.5 g, 6.92 mmol) in methanol (25 mL) was addedK₂CO₃ (1.43 g, 10.38 mmol) at rt. The reaction mixture was stirred for 1hour at rt., filtered and concentrated to give the crude product thatwas purified by column chromatography (petroleum ether/ethyl acetate;0-40% gradient) to give(S)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)but-3-yn-1-ol(70S) (1.4 g, 95%) as an orange liquid. C₁₁H₁₆O₄: ¹H NMR (500 MHz,CDCl₃): δ 5.82 (d, J=3.5 Hz, 1H), 4.76 (t, J=4.5 Hz, 1H), 4.33 (m, 1H),3.70 (m, 1H), 2.51-2.48 (m, 2H), 2.30 (d, J=6.5 Hz, 1H), 2.09 (dd,J=13.0, 4.5 Hz, 1H), 2.05 (t, J=2.5 Hz, 1H), 1.87 (m, 1H), 1.53 (s, 3H),1.26 (s, 3H).

Step 4:(S)-1-((3aR,5S,6aR)-2,2-Dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)but-3-yn-1-ylacetate (71S)

To a stirred solution of((S)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)but-3-yn-1-ol(70S) (1.32 g, 6.22 mmol), TEA (1.76 mL, 12.45 mmol), DMAP (0.151 g,1.24 mmol) in anhydrous CH₂Cl₂ (22 mL) was added acetic anhydride (0.92mL, 9.33 mmol). After being stirred at 25° C. for 10 h, the reaction wasadded to a saturated aq·NaHCO₃ solution (50 mL). The organic layer wasseparated and the aqueous phase was extracted with CH₂Cl₂ (2×50 mL). Thecombined organic layers were dried over anhydrous Na₂SO₄, filtered andconcentrated in vacuo. The crude mixture was purified by columnchromatography on silica gel (100-200 mesh, 30% EtOAc in petroleumether) to afford(S)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)but-3-yn-1-ylacetate (71S) (1.3 g, 83%) as a colorless oil. C₁₃H₁₈O₅: ¹H NMR (400MHz, CDCl₃): δ 5.82 (d, J=3.6 Hz, 1H), 5.03 (m, 1H), 4.75 (dd, J=8.0,3.6 Hz, 1H), 4.48 (m, 1H), 2.65-2.52 (m, 2H), 2.12 (s, 3H), 2.09 (m,1H), 2.07 (m, 1H), 1.65 (m, 1H), 1.52 (s, 3H), 1.33 (s, 3H).

Step 5:(2S,3R,5S)-5-((S)-1-Acetoxybut-3-yn-1-yl)tetrahydrofuran-2,3-diyldiacetate (72S)

To a solution of(S)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)but-3-yn-1-ylacetate (71S) (1.3 g, 5.11 mmol), acetic acid (3.0 mL, 51.18 mmol) andacetic anhydride (2.43 mL, 25.59 mmol) in anhydrous CH₂Cl₂ (50 mL) wasadded concentrated H₂SO₄ (0.2 mL) at 0° C. After being stirred at 25° C.for 3 hours, the pH of the reaction mixture was made basic by theaddition of saturated aq·NaHCO₃ solution (100 mL). The organic layer wasseparated and the aqueous phase was extracted with CH₂Cl₂ (2×100 mL).The combined organic layers were dried over Na₂SO₄, filtered andconcentrated in vacuum. The crude product was purified by columnchromatography on silica gel (100-200 mesh, 30% EtOAc in petroleumether) to afford(2R,3R,5S)-5-((S)-1-acetoxybut-3-yn-1-yl)tetrahydrofuran-2,3-diyldiacetate (72S) (700 mg, 46%) as a colorless oil. C₁₄H₁₈O₇: ¹H NMR (400MHz, CDCl₃): δ 6.13 (s, 1H), 5.19 (d, J=4.4 Hz, 1H), 5.00 (m, 1H), 4.59(m, 1H), 2.62-2.47 (m, 2H), 2.15-2.12 (m, 3H), 2.10 (s, 9H).

Step 6:(S)-1-((2S,4R,5R)-5-(2-Acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)but-3-yn-1-ylacetate (66)

N-(6,8-dioxo-7-(prop-2-yn-1-yl)-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide(6) (500 mg, 2.02 mmol),(2R,3R,5S)-5-((S)-1-acetoxybut-3-yn-1-yl)tetrahydrofuran-2,3-diyldiacetate (72S) (723 mg, 2.42 mmol), BSA (1.53 mL, 6.07 mmol) weredissolved in 1,2-dichloroethane (20 mL) and the reaction mixture wasstirred at 80° C. under argon. After 30 min. the reaction mixture wascooled to RT and 1,2-dichloroethane was removed under vacuum. Theresidue was dissolved in MeCN (20 mL) followed by addition of TMSOTf(0.55 mL, 3.03 mmol). The reaction mixture was heated at 80° C. for 16h, cooled to room temperature and concentrated under vacuum. To theresidue obtained was added sat. aq. NaHCO₃ (50 mL) and then extractedwith EtOAc (3×50 mL). The combined EtOAc extracts were washed with water(30 mL), brine (30 mL), dried over Na₂SO₄, filtered and concentratedunder vacuum. The crude product was purified by GRACE flashchromatography (80% EtOAc in pet ether) to afford 230 mg (34.6%) of(S)-1-((2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)but-3-yn-1-ylacetate (66) as a brown solid. C₂₂H₂₃N₅O₈: ES+, m/z 486.0 [M+H]⁺.

Step 7:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxybut-3-yn-1-yl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione(Compound 35)

To a solution of((S)-1-((2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)but-3-yn-1-ylacetate (66) (210 mg, 0.432 mmol) in MeOH (20 mL) was added K₂CO₃ (90mg, 0.649 mmol) at 0° C. and the reaction mixture was stirred at RT for16 h. Methanol was removed under reduced pressure at 30° C. The residuewas applied directly to reverse phase GRACE flash chromatography (using0.01% aq. NH₄HCO₃ and MeCN). The pure fractions were collected andlyophilized to afford 80 mg (46%) of2-amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxybut-3-yn-1-yl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione(Compound 35) as a white solid. C₁₆H₁₇N₅O₅: ¹H NMR (400 MHz, DMSO-d₆): δ10.95 (brs, 1H), 6.53 (brs, 2H), 5.53 (d, J=3.2 Hz, 1H), 5.42 (d, J=4.4Hz, 1H), 5.00 (d, J=6.8 Hz, 1H), 4.73 (m, 1H), 4.59 (s, 2H), 4.17 (m,1H), 3.57 (m, 1H), 3.22 (s, 1H), 2.74 (s, 1H), 2.43 (m, 1H), 2.33-2.26(m, 2H), 1.82 (m, 1H). ES+, m/z 360.0 [M+H]⁺.

Example 32:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-8H-purin-8-one,Compound 36

Compound 36 was prepared according to the following two step procedure.

Step 1:(R)-1-((2S,4R,5R)-5-(2-Acetamido-8-oxo-7-(prop-2-yn-1-yl)-7,8-dihydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2,2,2-trifluoroethylacetate (67A) and(S)-1-((2S,4R,5R)-5-(2-acetamido-8-oxo-7-(prop-2-yn-1-yl)-7,8-dihydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2,2,2-trifluoroethylacetate (67B)

To N-(8-oxo-7-(prop-2-yn-1-yl)-8,9-dihydro-7H-purin-2-yl)acetamide (21)(500 mg, 2.1 mmol) and(2S,3R,5S)-5-(1-acetoxy-2,2,2-trifluoroethyl)tetrahydrofuran-2,3-diyldiacetate (22S) (855 mg, 2.6 mmol) in 1,2-dichloroethane (20 mL) wasadded BSA (1.64 mL, 6.52 mmol). The reaction mixture was stirred at 80°C. for 30 min under argon, then allowed to cool to RT and1,2-dichloroethane was removed under vacuum. The residue was taken up inMeCN (20 mL) followed by addition of TMSOTf (0.6 mL, 3.2 mmol). Thereaction mixture was heated at 80° C. for 16 h, cooled to roomtemperature and concentrated under vacuum. To the residue was added sat.aq·NaHCO₃ (50 mL) and extracted with EtOAc (3×50 mL). The combined EtOAclayer were washed with water (30 mL), brine (30 mL), dried over Na₂SO₄,filtered and concentrated under vacuum. The crude product was purifiedby GRACE flash chromatography (80% EtOAc in pet ether) to afford 530 mgof a diastereomeric mixture of(R,S)-1-((2S,4R,5R)-5-(2-acetamido-8-oxo-7-(prop-2-yn-1-yl)-7,8-dihydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2,2,2-trifluoroethylacetate (˜1.7:1) as an off-white solid. Separation the diastereomers byPrep-HPLC (Column: X-SELECT-C18 (50*19), 5 u Mobile phase: 0.1% TFA inH₂O:MeCN Gradient: (T % B):—0/10, 8/50, 10/50, 10.1/98, 11/98, 11.1/10,13/10; Flow Rate: 17 mL/min) to give 230 mg of(R)-1-((2S,4R,5R)-5-(2-acetamido-8-oxo-7-(prop-2-yn-1-yl)-7,8-dihydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2,2,2-trifluoroethylacetate (67A) and 100 mg of(S)-1-((2S,4R,5R)-5-(2-acetamido-8-oxo-7-(prop-2-yn-1-yl)-7,8-dihydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2,2,2-trifluoroethylacetate(67B). (67A): C₂₀H₂₀F₃N₅O₇: ¹H NMR (500 MHz, DMSO-d₆): δ 8.42 (s, 1H),5.84 (d, J=1.0 Hz, 1H), 5.70 (m, 2H), 4.80 (d, J=2.5 Hz, 2H), 4.56 (m,2H), 3.46 (t, J=2.5 Hz, 1H), 3.29 (m, 1H), 2.18 (m, 1H), 2.12 (s, 3H),2.08 (s, 6H). ES+, m/z 499.9 [M+H]⁺. (67B): (*Loss of an —Ac group wasobserved by LC/MS and ¹H NMR after HPLC purification) C₁₈H₁₈F₃N₅O₆: ¹HNMR (400 MHz, DMSO-d₆): δ 8.14 (s, 1H), 7.40 (bs, 1H), 5.81 (d, J=2.0Hz, 1H), 5.75 (m, 2H), 4.80-4.60 (b, 1H), 4.67 (t, J=2.0 Hz, 2H), 4.59(m, 1H), 3.46 (t, J=2.4 Hz, 1H), 3.02-2.94 (m, 1H), 2.16 (dd, J=13.6 Hz,5.6 Hz, 1H), 2.09 (s, 3H), 2.08 (s, 3H). ES+, m/z 458.1 [M+H]⁺.

Step 2:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-8H-purin-8-one(Compound 36)

To a solution of(R)-1-((2S,4R,5R)-5-(2-acetamido-8-oxo-7-(prop-2-yn-1-yl)-7,8-dihydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2,2,2-trifluoroethylacetate (67A) (230 mg, 0.46 mmol) in MeOH (20 mL) was added K₂CO₃ (95mg, 0.69 mmol) at 0° C. The reaction mixture was stirred at rt for 16 h,and then methanol was removed under reduced pressure at 30° C. Theresidue was applied directly to reverse phase GRACE flash chromatography(10 mM ammonium bicarbonate in H₂O). The pure fractions were lyophilizedto yield 80 mg (46%) of2-amino-9-((2R,3R,5S)-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-8H-purin-8-one(Compound 36) as an off-white solid. C₁₄H₁₄F₃N₅O₄: ¹H NMR (500 MHz,DMSO-d₆): δ 8.04 (s, 1H), 6.37 (s, 2H), 6.29 (bs, 1H), 5.67 (d, J=2.5Hz, 1H), 5.58 (brs, 1H), 4.79 (m, 1H), 4.64 (d, J=2.0 Hz, 2H), 4.34 (m,1H), 4.06 (m, 1H), 3.41 (d, J 2.5 Hz, 1H), 2.62 (m, 1H), 1.96 (m, 1H).ES+, m/z 374.31 [M+H]⁺.

Example 33: Compound 37 and 382-Amino-9-((2R,3R,5S)-3-hydroxy-5-propionyltetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 37

2-Amino-9-((2R,3R,5R)-3-hydroxy-5-propionyltetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 38

Compounds 37 and 38 were prepared according to the following multi-stepprocedures.

Step 1:1-((3aR,5S,6aR)-2,2-Dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propan-1-one(73S)

To a solution of1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propan-1-ol(5S) (2.3 g, 11.38 mmol) in CH₂Cl₂ (46 mL), was added pyridiniumdichromate (5.14 g, 13.66 mmol) and acetic anhydride (2.3 mL, 1 vol) at0° C. The reaction mixture was monitored by TLC and stirred for 16 h atrt. The reaction mixture was concentrated and the residue was purifiedby column chromatography on silica gel (100-200 mesh, 50% EtOAc inpetroleum ether) to afford1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propan-1-one(73S) (2.1 g, 90%) as a pale yellow liquid. C₁₀H₁₆O₄: ¹H NMR (400 MHz,CDCl₃): δ 5.91 (d, J=3.6 Hz, 1H), 4.75 (t, J=4.2 Hz, 1H), 4.63 (dd,J=11.2, 4.8 Hz, 1H), 2.61 (dq, J=7.2, 2.0 Hz, 2H), 2.37 (dd, J=13.4, 5.0Hz, 1H), 1.76 (dd, J=15.8, 9.9, 3.5 Hz, 1H), 1.52 (s, 3H), 1.43 (s, 3H),1.05 (t, J=7.2 Hz, 3H).

Step 2: (2S,3R,5S)-5-Propionyltetrahydrofuran-2,3-diyl diacetate (74S)

To a solution of1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)propan-1-one(73S) (2.1 g, 10.48 mmol), acetic acid (6.34 mL, 104.87 mmol) and aceticanhydride (5.39 mL, 52.43 mmol) in anhydrous CH₂Cl₂ (40 mL) was addedconcentrated H₂SO₄ (0.1 mL) at 0° C. After being stirred at 25° C. for 3h, the pH of the reaction mixture was made basic by the addition of asaturated aq. NaHCO₃ solution (200 mL). The organic layer was separatedand the aqueous phase was extracted with CH₂C₂ (2×200 mL). The combinedorganic layers were dried over Na₂SO₄, filtered and concentrated invacuum. The crude product was purified by column chromatography onsilica gel (100-200 mesh, 20% EtOAc in petroleum ether) to affordpredominately (2S,3R,5S)-5-propionyltetrahydrofuran-2,3-diyl diacetate(74S) (1.3 g, 52%) as a colourless liquid. C₁₁H₁₆O₆: ¹H NMR (500 MHz,DMSO-d₆): δ 6.07 (d, J=2.0 Hz, 1H), 5.09 (t, J=3.0 Hz, 1H), 4.78 (t,J=8.3 Hz, 1H), 2.56-2.50 (m, 2H), 2.28 (dd, J=8.5, 3.5 Hz, 2H), 2.05 (s,3H), 2.01 (s, 3H), 0.93 (t, J=7.3 Hz, 3H).

Step 3:(2R,3R,5S)-2-(2-Acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-5-propionyltetrahydrofuran-3-ylacetate (68)

N-(6,8-dioxo-7-(prop-2-yn-1-yl)-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide(6) (500 mg, 2.024 mmol), (2S,3R,5S)-5-propionyltetrahydrofuran-2,3-diyldiacetate (74S) (692 mg, 2.83 mmol) and BSA (1.54 mL, 6.07 mmol) weredissolved in 1,2-dichloroethane (50 mL) and the reaction mixture wasstirred at 80° C. for 30 min under argon. The reaction mixture wascooled to rt and 1,2-dichloroethane was removed by vacuum. The residuewas dissolved in MeCN (50 mL) followed by addition of TMSOTf (0.561 mL,3.03 mmol). The reaction mixture was heated at 80° C. for 16 h, cooledto room temperature and concentrated under vacuum. To the residue wasadded sat. aq. NaHCO₃ (100 mL) and extracted with EtOAc (2×200 mL). Thecombined EtOAc layer was washed with water (50 mL), brine (50 mL), driedover Na₂SO₄, filtered and concentrated under vacuum. The crude compoundwas purified by flash column (80% EtOAc in pet ether) to afford(2R,3R,5S)-2-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-5-propionyltetrahydrofuran-3-ylacetate (68) (310 mg, 28%) as an off-white solid. C₁₉H₂₁N₅O₇: ES+, m/z432.2 [M+H]⁺.

Step 4:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-propionyltetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione(Compound 37) and2-Amino-9-((2R,3R,5R)-3-hydroxy-5-propionyltetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione(Compound 38)

To a stirred solution of(2R,3R,5S)-2-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-5-propionyltetrahydrofuran-3-ylacetate (68) (300 mg, 0.69 mmol) in methanol (10 mL) was added K₂CO₃ (96mg, 0.69 mmol) at room temperature. The progress of the reaction wasmonitored by LC/MS. After 16 hrs. LC/MS indicated complete conversion ofstarting material to the product along with some epimerization at C-5.The reaction mixture was concentrated under reduced pressure to afford asolid that was applied directly to GRACE reverse phase chromatography(0.1% HCO₂H:MeCN) to afford a diastereomeric mixture of2-amino-9-((2R,3R)-3-hydroxy-5-propionyltetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione(60 mg, 25%). This mixture was further purified by Chiral SFC-150-080HPLC (Chiralcel OJ-H OX-H; 250×30×5μ; 80% CO₂, 20% MeOH; Total Flow:90.0 g/min.; Back pressure: 100.0 bar; 30° C.; UV: 214.0 nm; Stack time:11.0 mins; Load/injection: 10.0 mgs) to give2-amino-9-((2R,3R,5S)-3-hydroxy-5-propionyltetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione(Compound 37) (15 mg) and2-amino-9-((2R,3R,5R)-3-hydroxy-5-propionyltetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione(Compound 38) (16 mg), both as off-white solids. (Compound 37):C₁₅H₁₇N₅O₅: ¹H NMR (400 MHz, DMSO-d₆): 11.56 (bs, 1H), 6.71 (s, 2H),5.66 (d, J=2.0 Hz, 1H), 5.56 (d, J=4.4 Hz, 1H), 4.75 (m, 1H), 4.60 (d,J=2.0 Hz, 2H), 4.53 (dd, J=9.0, 7.4 Hz, 1H), 3.19 (t, J=2.4 Hz, 1H),2.79-2.72 (m, 1H), 2.67-2.60 (m, 1H), 2.43 (dd, J=7.2, 4.4 Hz, 1H), 2.02(ddd, J=12.8, 7.2, 2.4 Hz, 1H), 0.87 (t, J=7.2 Hz, 3H). ES+, m/z 348.3[M+H]⁺. (Compound 38): C₁₅H₁₇N₅O₅: ¹H NMR (400 MHz, DMSO-d₆): δ 11.71(bs, 1H), 6.65 (bs, 2H), 5.73 (d, J=2.8 Hz, 1H), 5.50 (d, J=4.0 Hz, 1H),4.83 (s, 1H), 4.76 (t, J=7.6 Hz, 1H), 4.61 (s, 2H), 3.18 (m, 1H), 2.91(dt, J=12.4, 7.2 Hz, 1H), 2.66 (m, 1H), 2.60 (dd, J=16.8, 7.2 Hz, 1H),1.89 (m, 1H), 0.93 (t, J=7.2 Hz, 3H). ES+, m/z 348.3 [M+H]⁺.

Example 34:Methyl(2S,4R,5R)-5-(2-amino-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-hydroxytetrahydrofuran-2-carboxylate,Compound 39

Compound 39 was prepared according to the following multi-stepprocedure.

Step 1:((3aR,5S,6aR)-2,2-Dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)methanol(75S)

To a solution of(3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxole-5-carbaldehyde(4S) [4613-68-7] (20 g, 116.2 mmol) in EtOH (250 mL) was added NaBH₄(4.39 g, 28.0 mmol) while maintaining the temperature between 0-5° C.The reaction mixture was warmed to 10° C. and stirred for 2 h. EtOH wasremoved under vacuum and the residue was diluted with water (300 mL) andextracted with CHCl₃ (2×300 mL). The combined organic layers were driedover Na₂SO₄, filtered, and concentrated under reduced pressure. Theresidue was purified by column chromatography on silica gel (100-200mesh, 50% EtOAc in pet-ether) to give((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)methanol(75S) [3396-71-2] (8.8 g, 43%) as a white solid. C₈H₁₄O₄: ¹H NMR (400MHz, CDCl₃): δ 5.83 (d, J=3.6 Hz, 1H), 4.76 (t, J=4.2 Hz, 1H), 4.35 (m,1H), 3.90 (dd. J=12.2, 2.6 Hz, 1H). 3.57 (dd, J=12.0, 3.6 Hz, 1H), 2.01(dd, J=13.4, 4.6 Hz, 1H), 1.88 (bs, 1H), 1.87-1.81 (m, 1H), 1.52 (s,3H), 1.33 (s, 3H). ES+, m/z 175.1 [M+H]⁺.

Step 2:(3aR,5S,6aR)-2,2-Dimethyltetrahydrofuro[2,3-d][1,3]dioxole-5-carboxylicacid (76S)

A mixture of((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)methanol(75S) [3396-71-2] (3.1 g, 17.8 mmol), ruthenium oxide (228 mg), andsodium periodate (15.22 g, 213.8 mmol) in acetonitrile:chloroform:water(24:24:36 mL) was stirred vigorously for 4-6 h at room temperature.After separation of the two layers, the aqueous layer was extracted withchloroform (3×50 mL). The combined organic layers were washed withbrine, dried over anhydrous Na₂SO₄, filtered and concentrated to drynessin vacuum to give(3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxole-5-carboxylicacid (76S) [163042-94-2] (3.0 g, 89%) as a black liquid. The crudeproduct was used in the next step without purification.

Step 3: Methyl(3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxole-5-carboxylate(77S)

A mixture of(3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxole-5-carboxylicacid (76S) [163042-94-2] (3.0 g, 18.95 mmol), EDCI·HCl (7.61 g, 39.89mmol), and DMAP (194 mg, 1.59 mmol) in anhydrous methanol (50 mL) wasstirred for 24 h at room temperature. MeOH was removed under vacuum andthe residue obtained was dissolved in CH₂Cl₂ (100 mL) and washed withwater (2×50 mL). The layers were separated and the aqueous phase wasextracted with CH₂Cl₂ (3×30 mL). The combined organic layer were washedwith brine, dried over anhydrous NaSO₄, filtered and concentrated todryness. The residue was purified by column chromatography on silica gel(100-200 mesh, 20% EtOAc in pet-ether) to give methyl(3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxole-5-carboxylate(77S) [126694-09-5] (2.5 g, 78%) as a colourless liquid. C₉H₁₄O₅: ¹H NMR(500 MHz, CDCl₃): δ 5.95 (d, J=3.5 Hz, 1H), 4.78 (t, J=4.0 Hz, 1H), 4.71(dd, J=11.0, 5.0 Hz, 1H), 3.78 (s, 3H), 2.42 (dd, J=13.5, 5.0 Hz, 1H),1.96 (ddd, J=14.5, 10.0, 3.5 Hz, 1H), 1.52 (s, 3H), 1.33 (s, 3H).

Step 4: (2S,3R,5S)-5-(Methoxycarbonyl)tetrahydrofuran-2,3-diyl diacetate(78S)

To a solution of methyl(3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxole-5-carboxylate(77S) [126694-09-5] (2.0 g, 9.9 mmol), acetic acid (5.66 mL, 99 mmol)and acetic anhydride (4.9 mL, 49.5 mmol) in anhydrous CH₂Cl₂ (30 mL) wasadded concentrated H₂SO₄ (0.2 mL) at 0° C. After being stirred at RT for3 hours, the pH of reaction mixture was made basic by the addition ofsaturated aq. NaHCO₃ solution (100 mL). The organic layer was separatedand the aqueous phase was extracted with CH₂Cl₂ (2×100 mL). The combinedorganic layers were dried over Na₂SO₄, filtered and concentrated invacuum. The crude product was purified by column chromatography onsilica gel (100-200 mesh, 40% EtOAc in petroleum ether) to afford 1.4 g(58%) of (2S,3R,5S)-5-(methoxycarbonyl)tetrahydrofuran-2,3-diyldiacetate (78S) as a colorless oil. C₁₀H₁₄O₇: ¹H NMR (400 MHz, CDCl₃): δ6.21 (s, 1H), 5.21 (d, J=4.8 Hz, 1H), 4.82 (t, J=8.2 Hz, 1H), 3.77 (s,3H), 2.51-2.39 (m, 2H), 2.15 (s, 3H), 2.07 (s, 3H).

Step 5: Methyl(2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-carboxylate(69)

N-(6,8-Dioxo-7-(prop-2-yn-1-yl)-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide(6) (200.8 mg, 0.813 mmol),((2S,3R,5S)-5-(methoxycarbonyl)tetrahydrofuran-2,3-diyl diacetate (78S)(200 mg, 0.813 mmol) and BSA (0.6 mL, 2.43 mmol) were dissolved in1,2-dichloroethane (10 mL) and the reaction mixture was stirred at 80°C. for 30 min under argon. The reaction mixture was allowed then cooledto RT and 1,2-dichloroethane was removed under vacuum. The residue wasdissolved in MeCN (20 mL) and TMSOTf (0.26 mL, 1.21 mmol) was added. Thereaction mixture was heated at 80° C. for 16 h, cooled to roomtemperature and concentrated under vacuum. To the residue was added sat.aq. NaHCO₃ (50 mL) and then extracted with EtOAc (3×50 mL). The combinedEtOAc layers were washed with water (30 mL), brine (30 mL), dried overanhydrous Na₂SO₄, filtered and concentrated under vacuum. The crudeproduct was purified by GRACE flash chromatography (80% EtOAc in petether) to afford 150 mg (34.6%) of methyl(2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-carboxylate(69) as an brown solid. C₁₈H₁₉N₅O₈: H NMR (400 MHz, DMSO-d₆): δ 12.20(s, 1H), 11.67 (s, 1H), 5.81 (d, J=1.2 Hz, 1H), 5.76 (t, J=3.4 Hz, 1H),4.86 (t, J=8.2 Hz, 1H), 4.67 (d, J=2.4 Hz, 2H), 3.64 (m, 1H), 3.31 (s,3H), 3.17 (m, 1H), 2.41 (m, 1H), 2.19 (s, 3H), 2.08 (s, 3H). ES+, m/z434.2 [M+H]⁺.

Step 6: Methyl(2S,4R,5R)-5-(2-amino-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-hydroxytetrahydrofuran-2-carboxylate(Compound 39)

To a solution of methyl(2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-carboxylate(69) (150 mg, 0.346 mmol) in MeOH (20 mL) was added K₂CO₃ (47.8 mg,0.346 mmol) at 0° C. The reaction mixture was stirred at RT for 16 h andthen methanol was removed under reduced pressure at 30° C. The residueobtained was subjected directly to reverse phase prep-HPLC (usingX-BRIDGE-C₁₈ (250*19), 5 u Mobile phase: 0.1% HCO₂H in H₂O:MeCN;Gradient: (T % B):—0/5, 28/5, 8/40, 9/40, 9.10/98, 11/98, 14/5; Flowrate: 18 mL/min.; Diluent: MeCN+H₂O+THF). The pure fractions werelyophilized to afford 32 mg (30%) of methyl(2S,4R,5R)-5-(2-amino-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-hydroxytetrahydrofuran-2-carboxylate(Compound 39) as a white solid. C₁₄H₁₅N₅O₆: ¹H NMR (500 MHz, DMSO-d₆): δ10.85 (brs, 1H), 6.56 (brs, 2H), 5.62 (d, J=2.0 Hz, 1H), 5.58 (d, J=4.0Hz, 1H), 4.84 (m, 1H), 4.72 (t, J=8.0 Hz, 1H), 4.57 (d, J=2.0 Hz, 2H),3.60 (s, 3H), 3.22 (t, J=2.3 Hz, 1H), 2.87 (m, 1H), 2.12 (ddd, J=12.8,7.3, 2.0 Hz, 1H). ES+, m/z 350.2 [M+H]⁺.

Example 35:(2S,4R,5R)-5-(2-Amino-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-hydroxytetrahydrofuran-2-carboxylicacid, Compound 40

Compound 40 was prepared according to the following procedure.

Step 1:(2S,4R,5R)-5-(2-Amino-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-hydroxytetrahydrofuran-2-carboxylicacid (Compound 40)

To a solution of methyl(2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-carboxylate(Compound 39) (300 mg, 0.692 mmol) in THF:MeOH:H₂O (8:4:4 mL) was addedLiOH (116 mg, 2.77 mmol) at 0° C. The reaction mixture was warmed to RTand stirred for 16 h. The solvents was removed under reduced pressure at30° C. and the residue was subjected directly to reverse phase prep-HPLC(using X-SELECT-C18 (250*19), 5 u Mobile phase: 0.1% HCO₂H in H₂O:MeCNGradient: (T % B):—0/2, 2/2, 6/5, 10/30, 14/45, 14.1/98, 16/98, 16.1/2,20/20; Flow rate: 16 mL/min; Diluent: MeOH+H₂O+THF). The pure fractionswere subjected to lyophilization to yield 32 mg (30%) of(2S,4R,5R)-5-(2-amino-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-hydroxytetrahydrofuran-2-carboxylicacid, (Compound 40) as an white solid. C₁₃H₁₃N₅O₆: ¹H NMR (400 MHz,DMSO-d₆): 9.12 (brs, 1H), 6.71 (brs, 2H), 5.50 (d, J=2.0 Hz, 1H), 5.41(bs, 1H), 4.80 (m, 1H), 4.58 (d, J=2.0 Hz, 2H), 4.40 (dd, J=10.0 Hz, 6.4Hz, 1H), 3.19 (t, J=2.4 Hz, 1H), 2.67-2.59 (m, 1H), 2.00 (dd, J=12.2,7.0 Hz, 1H). ES+, m/z 336.2 [M+H]⁺.

Example 36:(2S,4R,5R)-5-(2-Amino-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-hydroxytetrahydrofuran-2-carboxamide,Compound 41

Compound 41 was prepared according to the following procedure.

Step 1:(2S,4R,5R)-5-(2-Amino-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-hydroxytetrahydrofuran-2-carboxamide(Compound 41)

To a solution of methyl(2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-carboxylate(Compound 39) (100 mg, 0.23 mmol) in methanol (5 mL) was added 7 Nammonia in methanol (5 mL) at 0° C. The reaction mixture was stirred ina sealed vessel at 100° C. for 16 h. The reaction mixture was cooled andvented carefully, and the solvent was removed under reduced pressure at30° C. The residue was subjected directly to reverse phase prep-HPLC(using LUNA OMEGA C18 (250*21.2), 5 u Mobile phase: 0.1% HCO₂H inH₂O:MeCN Gradient: (T % B):—0/2, 2/2, 8/40, 10/40, 10.1/98, 13/98,13.1/2, 16/2; Flow rate: 16 mL/min.; Diluent: MeCN+H₂O+THF). The purefractions were lyophilized to give 25 mg (32%) of(2S,4R,5R)-5-(2-amino-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-hydroxytetrahydrofuran-2-carboxamide (Compound 41) as an off-white solid.C₁₃H₁₄N₆O₅: ¹H NMR indicated formation of the formic acid salt. ¹H NMR(500 MHz, DMSO-d₆): δ 12.48 (brs, 1H), 8.48 (brs, 2H), 7.75 (bs, 1H),7.18 (s, 1H), 7.09 (m, 2H), 5.60 (bs, 1H), 5.55 (d, J=5.0 Hz, 1H), 4.77(m, 1H), 4.62 (s, 2H), 4.34 (dd, J=8.5, 6.0 Hz, 1H) 3.22 (t, J=2.2 Hz,1H), 2.40 (m, 1H), 2.20 (m, 1H). ES+, m/z 335.22 [M+H]⁺.

Example 37:(2S,4R,5R)-5-(2-Amino-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-hydroxy-N-methyltetrahydrofuran-2-carboxamide,Compound 42

Compound 42 was prepared according to the following procedure.

Step 1:(2S,4R,5R)-5-(2-Amino-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-hydroxy-N-methyltetrahydrofuran-2-carboxamide(Compound 42)

To a solution of methyl(2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-carboxylate(Compound 39) (100 mg, 0.23 mmol) in THE (4 mL) was added methylamine inTHE (2M)(3 mL) at 0° C. The reaction mixture was stirred in a sealedvessel at 100° C. for 16 h. The reaction mixture was cooled and ventedcarefully, and the solvent was removed under reduced pressure at 30° C.The residue was subjected directly to reverse phase GRACE flashchromatography (0.1% NH₄HCO₃ in H₂O:MeCN). The pure fractions werelyophilized to give 22 mg (32%) of(2S,4R,5R)-5-(2-amino-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-hydroxy-N-methyltetrahydrofuran-2-carboxamide(Compound 42) as an off-white solid. C₁₄H₁₆N₆O₅: ¹H NMR (500 MHz,DMSO-d₆): δ 11.04 (brs, 1H), 7.69 (d, J=4.5 Hz, 1H), 6.59 (s, 2H), 5.57(dd, J=12.8, 4.3 Hz, 2H), 4.80 (m, 1H), 4.61 (d, J=1.0 Hz, 2H), 4.43 (t,J=7.8 Hz, 1H), 3.24 (t, J=2.3 Hz, 1H), 2.61 (d, J=4.5 Hz, 3H), 2.53 (m,1H), 2.15 (m, 1H). ES+, m/z 349.0[M+H]⁺.

Example 38:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(2,2,2-trifluoroethyl)-7,9-dihydro-1H-purine-6,8-dione,Compound 43

Compound 43 was prepared according to the following multi-stepprocedure.

Step 1:2-Amino-6-(benzyloxy)-9-(4-methoxybenzyl)-7-(2,2,2-trifluoroethyl)-7,9-dihydro-8H-purin-8-one(70)

2-Bromo-1,1,1-trifluoroethane (4.5 g, 27.85 mmol) was added to asuspension of2-amino-6-(benzyloxy)-9-(4-methoxybenzyl)-7,9-dihydro-8H-purin-8-one (6)(7 g, 18.5 mmol) and K₂CO₃ (6.4 g, 46.41 mmol) in DMF (70 mL) at rt andstirred in sealed tube at 70° C. for 16 h. The reaction mixture wascooled to rt and ice water (500 mL) was added. The resultingprecipitated solid was filtered, washed with water and diethyl ether(200 mL) and dried to afford2-amino-6-(benzyloxy)-9-(4-methoxybenzyl)-7-(2,2,2-trifluoroethyl)-7,9-dihydro-8H-purin-8-one(70) (6.4 g, 75%) as an off white solid. C₂₂H₂₀F₃N₅O₃: ¹H NMR (400 MHz,DMSO-d₆): δ 7.46 (d, J=7.6 Hz, 2H), 7.41-7.31 (m, 3H), 7.23 (d, J=8.4Hz, 2H), 6.89 (d, J=8.8 Hz, 2H), 6.54 (s, 2H), 5.42 (s, 2H), 4.85 (s,2H), 4.55 (m, 2H), 3.71 (s, 3H). ES+, m/z 460.1 [M+H]⁺.

Step 2: 2-Amino-7-(2,2,2-trifluoroethyl)-7,9-dihydro-1H-purine-6,8-dione(71)

Trifluoromethanesulfonic acid (7.3 mL, 83.6 mmol) was added to asuspension of2-amino-6-(benzyloxy)-9-(4-methoxybenzyl)-7-(2,2,2-trifluoroethyl)-7,9-dihydro-8H-purin-8-one(70) (6.4 g, 13.94 mmol) in TFA (6.8 mL, 83.6 mmol) at room temperatureunder an argon atmosphere. The reaction mixture was stirred at roomtemperature for 16 h under argon atmosphere at which time ice cold waterwas added and the pH of the mixture was made basic with a sat. NaHCO₃solution. Vigorous stirring was continued and the mixture was thenfiltered. The solid was taken up in ethyl acetate, stirred for 30 min.,filtered and dried to afford2-amino-7-(2,2,2-trifluoroethyl)-7,9-dihydro-1H-purine-6,8-dione (71)(2.4 g, 70%) as a brown solid. C₇H₆F₃N₅O₂: ¹H NMR (400 MHz, DMSO-d₆): δ11.37 (s, 1H), 10.78 (s, 1H), 6.46 (s, 2H), 4.53 (m, 2H). ES+, m/z 250.0[M+H]⁺.

Step 3:N-(6,8-Dioxo-7-(2,2,2-trifluoroethyl)-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide(72)

Acetic anhydride (2.86 mL, 28.9 mmol) was added to a solution of2-amino-7-(2,2,2-trifluoroethyl)-7,9-dihydro-1H-purine-6,8-dione (71)(2.4 g, 9.63 mmol) in AcOH (30 mL) at room temperature under an argonatmosphere and the resulting reaction mixture was stirred at 120° C. for16 h. The stirred reaction mixture was cooled to 0° C. whereupon a solidformed. After being stirred for 30 minutes the product was filtered,washed with diethyl ether and dried under vacuum to affordN-(6,8-dioxo-7-(2,2,2-trifluoroethyl)-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide(72) (2.1 g, 75%) as a brown solid. C₉H₈F₃N₅O₃: ¹H NMR (400 MHz,DMSO-d₆): δ 12.07 (s, 1H), 11.97 (s, 1H), 11.70 (s, 1H), 4.62 (q, J=8.8Hz, 2H), 2.16 (s, 3H). ES+, m/z 292.0 [M+H]⁺.

Step 4:(S)-1-((2S,4R,5R)-5-(2-Acetamido-6,8-dioxo-7-(2,2,2-trifluoroethyl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)propylacetate (73)

A mixture ofN-(6,8-dioxo-7-(2,2,2-trifluoroethyl)-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide(72) (400 mg, 1.37 mmol),(3R,5S)-5-((S)-1-acetoxypropyl)tetrahydrofuran-2,3-diyl diacetate (14S)(475 mg, 1.64 mmol) and BSA (1.04 mL, 4.12 mmol) dissolved in1,2-dichloroethane (25 mL) was stirred at 80° C. for 30 min under argon.The reaction mixture was allowed to cooled to RT and 1,2-dichloroethanewas removed under vacuum. The residue was dissolved in MeCN (25 mL) andTMSOTf (0.38 mL, 2.06 mmol) was added. The stirred reaction mixture washeated at 80° C. for 16 h, cooled to room temperature and concentratedunder vacuum. The residue was diluted with sat. aq. NaHCO₃ (60 mL) andextracted with EtOAc (3×50 mL). The combined EtOAc layer was washed withwater (20 mL), brine (20 mL), dried over anhydrous Na₂SO₄, filtered andconcentrated under vacuum. The crude product was purified by silica-gelcolumn chromatography (80% EtOAc in Pet ether) to afford(S)-1-((2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(2,2,2-trifluoroethyl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)propylacetate (73) (180 mg, 25%) as a light yellow solid. C₂₀H₂₄F₃N₅O₈: ¹H NMR(500 MHz, CDCl3): δ 9.00 (s, 1H), 5.83 (d, J=2.5 Hz, 1H), 5.68 (m, 1H),5.19 (m, 1H), 4.66 (m, 8.8 2H), 4.35 (m, 1H), 2.55 (m, 1H), 2.28 (s,3H), 2.12 (m, 2H), 2.10 (s, 3H), 2.06 (s, 3H), 1.56-1.69 (m, 2H), 0.93(t, J=7.5 Hz, 3H). ES+, m/z 520.1 [M+H]⁺.

Step 5:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(2,2,2-trifluoroethyl)-7,9-dihydro-1H-purine-6,8-dione(Compound 43)

To a solution of(S)-1-((2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(2,2,2-trifluoroethyl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)propylacetate (73) (180 mg, 0.34 mmol) in methanol (10 mL) at rt was addedK₂CO₃ (71.7 mg, 0.52 mmol). The progress of the reaction was followed byLC/MS. After the reaction mixture was stirred at room temperature for 16h. it was concentrated under reduced pressure, and the crude product waspurified by Prep-HPLC: Column; KROMOSIL-C18 (150*25 MM), 7 u Mobilephase: 10 mM ammonium bicarbonate in H₂O:MeCN; Gradient: (T % B) 0/5,2/5, 8/40, 9/40, 9.1/98, 14/98, 14.1/5, 16/5; Flow Rate: 22 mL/min. toafford2-amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(2,2,2-trifluoroethyl)-7,9-dihydro-1H-purine-6,8-dione(Compound 43) (55 mg, 40.4%) as an off-white solid. C₁₄H₁₈F₃N₅O₅: ¹H NMR(400 MHz, DMSO-d₆): δ 11.09 (s, 1H), 6.62 (s, 2H), 5.52 (d, J=2.8 Hz,1H), 5.40 (d, J=4.8 Hz, 1H), 4.73 (m, 1H), 4.61 (q, J=8.8 Hz, 2H), 4.53(d, J=6.8 Hz, 1H), 4.00 (dt, J=8.8, 6.0 Hz, 1H), 3.27 (m, 1H), 2.42-2.35(m, 1H), 1.76 (ddd, J=12.4, 6.4, 2.8 Hz, 1H), 1.43-1.37 (m, 1H),1.30-1.22 (m, 1H), 0.87 (t J=7.2 Hz, 3H). ES+, m/z 394.1 [M+H]⁺.

Example 39:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(2,2,2-trifluoroethyl)-7,9-dihydro-1H-purine-6,8-dione,Compound 44

Compound 44 was prepared according to the following two step procedure.

Step 1:(S)-1-((2R,3S,4S,5R)-5-(2-Acetamido-6,8-dioxo-7-(2,2,2-trifluoroethyl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxy-3-fluorotetrahydrofuran-2-yl)propylacetate (74)

ToN-(6,8-dioxo-7-(2,2,2-trifluoroethyl)-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide(72) (400 mg, 1.37 mmol),(3S,4S,5R)-5-((S)-1-acetoxypropyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate (37S) (504.7 mg, 1.64 mmol) in 1,2-dichloroethane (25 mL), wasadded BSA (1.04 mL, 4.12 mmol). The reaction mixture was stirred at 80°C. for 30 min under argon, allowed to cool to RT and 1,2-dichloroethanewas removed under vacuum. The residue was dissolved in MeCN (25 mL) andTMSOTf (0.38 mL, 2.06 mmol) was added. The reaction mixture was heatedat 80° C. for 16 h, cooled to room temperature and concentrated undervacuum. To the residue was added sat. aq. NaHCO₃ (60 mL) and the mixturewas extracted with EtOAc (3×30 mL). The combined EtOAc layer was washedwith water (25 mL), brine (25 mL), dried over anhydrous Na₂SO₄, filteredand concentrated under vacuum. The crude product was purified by columnchromatography on silica gel (80% EtOAc in Pet ether) to afford(S)-1-((2R,3S,4S,5R)-5-(2-acetamido-6,8-dioxo-7-(2,2,2-trifluoroethyl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxy-3-fluorotetrahydrofuran-2-yl)propylacetate (74) (225 mg, 30.4%) as a brown solid. C₂₀H₂₃F₄N₅O₈: ¹H NMR (400MHz, CDCl₃): δ 9.50 (s, 1H), 5.84 (m, 2H), 5.72 (m, 1H), 5.22 (m, 1H),5.00-5.14 (m, 1H), 4.68 (m, 1H), 4.26 (m, 1H), 2.30 (s, 3H), 2.15 (s,3H), 2.10 (s, 3H), 2.02 (m, 1H), 1.68-1.78 (m, 2H), 0.98 (t, J=7.4 Hz,3H). ES+, m/z 538.1 [M+H]⁺.

Step 2:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(2,2,2-trifluoroethyl)-7,9-dihydro-1H-purine-6,8-dione(Compound 44)

To(S)-1-((2R,3S,4S,5R)-5-(2-acetamido-6,8-dioxo-7-(2,2,2-trifluoroethyl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxy-3-fluorotetrahydrofuran-2-yl)propylacetate (74) (225 mg, 0.41 mmol) in methanol (10 mL) was added K₂CO₃(86.7 mg, 1.22 mmol) at rt. The progress of the reaction was followed beLC/MS. After the mixture was stirred at room temperature for about 16 h.it was concentrated under reduced the vacuum to afford a thick paste.The crude product was purified by GRACE reverse phase chromatography(0.1% ammonium bicarbonate:MeCN) to afford2-amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(2,2,2-trifluoroethyl)-7,9-dihydro-1H-purine-6,8-dione(Compound 44) (95 mg, 55%) as an off-white solid. C₁₄H₁₇F₄N₅O₅: ¹H NMR(400 MHz, DMSO-d₆, D₂O): δ 5.43 (d, J=7.2 Hz, 1H), 5.27 (ddd, J=34.4,7.2, 4.4 Hz, 1H), 5.06 (ddd, J=54.2, 6.0, 4.6 Hz, 1H), 4.70 (q, J=9.2Hz, 2H), 3.96 (ddd, J=15.6, 6.0, 4.8 Hz, 1H), 3.44 (m, 1H), 1.46-1.35(m, 2H), 0.90 (t, J=7.4 Hz, 3H). ES+, m/z 412.1 [M+H]⁺.

Example 40:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((R)-1-hydroxy-2-(methylthio)ethyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 45

Compound 45 was prepared according to the following multi-stepprocedure.

Step 1:(R)-1-((3aR,5S,6aR)-2,2-Dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)-2-(methylthio)ethan-1-ol(79S)

To a stirred solution of(3aR,5S,6aR)-2,2-dimethyl-5-((S)-oxiran-2-yl)tetrahydrofuro[2,3-d][1,3]dioxole(51S) (2.0 g, 10.75 mmol) in DMF (20 mL, 10 vol) was added sodiummethanethiolate (1.5 g, 21.50 mmol) at 0° C. The reaction was monitoredby TLC. After being stirred at 25° C. for 2 h the reaction mixture waspoured into ice cold water (200 ml) and the aqueous phase was extractedwith EtOAc (2×100 mL). The combined organic layers were dried overanhydrous Na₂SO₄, filtered and concentrated in vacuum. The crude productwas purified by column chromatography over silica gel (100-200 mesh, 25%EtOAc in petroleum ether) to afford(R)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)-2-(methylthio)ethan-1-ol(79S) (1.6 g, 64%) as a viscous oil. C₁₀H₁₈O₄S: ¹H NMR (400 MHz,DMSO-d₆): δ 5.72 (d, J=3.6 Hz, 1H), 4.91 (d, J=6.4 Hz, 1H), 4.71 (t,J=4.2 Hz, 1H), 4.16 (dt, J=10.4, 4.2 Hz, 1H), 3.51 (m, 1H), 2.58-2.50(m, 2H), 2.08 (s, 3H), 1.86 (m, 1H), 1.79-1.74 (m, 1H), 1.38 (s, 3H),1.23 (s, 3H).

Step 2:(R)-1-((3aR,5S,6aR)-2,2-Dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)-2-(methylthio)ethylacetate (80S)

To a stirred solution of(R)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)-2-(methylthio)ethan-1-ol(79S) (1.3 g, 5.55 mmol), TEA (2.4 mL, 16.65 mmol) and DMAP (0.135 g,1.11 mmol) in anhydrous CH₂Cl₂ (26 mL) was added acetic anhydride (1.13mL, 11.11 mmol). The reaction mixture was stirred at 25° C. for 16 h,poured into water (60 mL) and the organic layer was separated. Theaqueous phase was extracted with CH₂Cl₂ (2×60 mL). The combined organiclayers were dried over anhydrous Na₂SO₄, filtered and concentrated undervacuum. The crude product was purified by column chromatography onsilica gel (100-200 mesh, 20% EtOAc in petroleum ether) to afford(R)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)-2-(methylthio)ethylacetate (80S) (1.2 g, 78%) as a viscous oil. C₁₂H₂₀O₅S: ¹H NMR (400 MHz,CDCl₃): δ 5.82 (d, J=3.6 Hz 1H), 5.05 (ddd, J=7.2, 6.2, 3.8 Hz, 1H),4.74 (t, J=4.2 Hz, 1H), 4.49 (dt, J=10.8, 4.2 Hz, 1H), 2.76 (ddd,J=14.0, 7.6, 6.0 Hz, 2H), 2.15 (s, 3H), 2.12 (s, 3H), 2.06 (dd, J=13.2,4.4 Hz, 1H), 1.68-1.61 (m, 1H), 1.52 (s, 3H), 1.32 (s, 3H).

Step 3:(3R,5S)-5-((R)-1-Acetoxy-2-(methylthio)ethyl)tetrahydrofuran-2,3-diyldiacetate (81S)

To a solution of(R)-1-((3aR,5S,6aR)-2,2-dimethyltetrahydrofuro[2,3-d][1,3]dioxol-5-yl)-2-(methylthio)ethylacetate (80S) (1.2 g, 4.34 mmol), acetic acid (1.57 mL, 26.086 mmol) andacetic anhydride (2.68 mL, 26.08 mmol) in anhydrous CH₂Cl₂ (24 mL) wasadded concentrated H₂SO₄ (0.12 mL) at 0° C. The reaction mixture wasstirred at 25° C. for 4 h, and then the pH was made basic by theaddition of saturated aq·NaHCO₃ solution (200 mL). The organic layer wasseparated and the aqueous phase was extracted with CH₂Cl₂ (2×200 mL).The combined organic layers were dried over Na₂SO₄, filtered andconcentrated in vacuum. The crude product was purified by columnchromatography on silica gel (100-200 mesh, 20% EtOAc in petroleumether) to afford(3R,5S)-5-((R)-1-acetoxy-2-(methylthio)ethyl)tetrahydrofuran-2,3-diyldiacetate (81S) (600 mg, 43%) as a viscous oil. C₁₃H₂₀O₇S: ¹H NMR (400MHz, CDCl₃): δ 6.12 (s, 1H), 5.18 (d, J=4.4 Hz, 1H), 5.02 (m, 1H), 4.61(m, 1H), 2.75-2.68 (m, 2H), 2.15 (s, 3H), 2.12 (s, 3H), 2.10 (s, 3H),2.09 (s, 3H), 2.05 (m, 2H).

Step 4:(R)-1-((2S,4R,5R)-5-(2-Acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2-(methylthio)ethylacetate (75)

N-(6,8-dioxo-7-(prop-2-yn-1-yl)-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide(6) (350 mg, 1.417 mmol),(3R,5S)-5-((R)-1-acetoxy-2-(methylthio)ethyl)tetrahydrofuran-2,3-diyldiacetate (81S) (544 mg, 1.700 mmol) and BSA (1.078 mL, 4.251 mmol) weredissolved in 1,2-dichloroethane (25 mL) and the reaction mixture wasstirred at 80° C. for 30 min under argon. The reaction mixture wascooled to RT and 1,2-dichloroethane was evaporated under vacuum. Theresidue was dissolved in MeCN (25 mL) followed by the addition of TMSOTf(0.393 mL, 2.125 mmol). The reaction mixture was heated at 80° C. for 16h, cooled to room temperature and concentrated under vacuum. To theresidue was added sat. aq. NaHCO₃ (50 mL) and extracted with EtOAc (3×60mL). The combined EtOAc layer was washed with water (50 mL), brine (40mL), dried over anhydrous Na₂SO₄, filtered and concentrated undervacuum. The crude product was purified by flash column chromatography(90% EtOAc in Pet ether) to afford(R)-1-((2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2-(methylthio)ethylacetate (75) (180 mg, 25%) as an off-white solid. C₂₁H₂₅N₅O₈S: ¹H NMR(400 MHz, DMSO-d₆): δ 12.18 (s, 1H), 11.64 (s, 1H), 5.69 (d, J=1.6 Hz,1H), 5.67 (d, J=4.0 Hz, 1H), 5.04 (m, 1H), 4.67 (d, J=2.4 Hz, 2H), 4.38(m, 1H), 3.29 (t, J=2.4 Hz, 2H), 2.75 (m, 2H), 2.64 (dd, J=14.0, 8.4 Hz,1H), 2.19 (s, 3H), 2.10 (s, 3H), 2.07 (s, 3H), 1.91 (s, 3H). ES+, m/z508.1 [M+H]⁺.

Step 5:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((R)-1-hydroxy-2-(methylthio)ethyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,(Compound 45)

To a solution of(R)-1-((2S,4R,5R)-5-(2-acetamido-6,8-dioxo-7-(prop-2-yn-1-yl)-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxytetrahydrofuran-2-yl)-2-(methylthio)ethylacetate (75) (160 mg, 0.315 mmol) in methanol (10 mL) at roomtemperature was added K₂CO₃ (87 mg, 0.631 mmol). The reaction wasmonitored by LC/MS and after stirring for ˜16 h the mixture wasconcentrated under vacuum to afford a thick pastey solid. The crudeproduct was purified by GRACE reverse phase chromatography (0.1%HCO₂H:MeCN) to afford2-amino-9-((2R,3R,5S)-3-hydroxy-5-((R)-1-hydroxy-2-(methylthio)ethyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione(Compound 45) (55 mg, 45%) as an off-white solid. C₁₅H₁₉N₅O₅S: ¹H NMR(400 MHz, DMSO-d₆): δ 10.97 (s, 1H), 6.53 (s, 2H), 5.52 (d, J=3.2 Hz,1H), 5.43 (d, J=4.4 Hz, 1H), 4.95 (d, J=7.2 Hz, 1H), 4.75 (m, 1H), 4.59(d, J=2.4 Hz, 2H), 4.19 (m, 1H), 3.57 (m, 1H), 3.23 (t, J=2.4 Hz, 1H),2.56 (dd, J=13.2, 4.8 Hz, 1H), 2.46-2.40 (m, 2H), 2.06 (s, 3H), 1.83 (m,1H). ES+, m/z 382.2 [M+H]⁺.

Example 41:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(2-(methylthio)ethyl)-7,9-dihydro-1H-purine-6,8-dione,Compound 46

Compound 46 was prepared according to the following two step procedure.

Step 1:(S)-1-((2R,3S,4S,5R)-5-(2-Acetamido-7-(2-(methylthio)ethyl)-6,8-dioxo-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxy-3-fluorotetrahydrofuran-2-yl)propylacetate (76)

ToN-(7-(2-(methylthio)ethyl)-6,8-dioxo-6,7,8,9-tetrahydro-1H-purin-2-yl)acetamide(37) (400 mg, 1.41 mmol) and(3S,4S,5R)-5-((S)-1-acetoxypropyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate (37S) (519 mg, 1.69 mmol) in 1,2-dichloroethane (25 mL) wasadded BSA (1.07 mL, 4.24 mmol). The reaction mixture was stirred at 80°C. for 30 min under argon, cooled to RT and 1,2-dichloroethane wasremoved under vacuum. The residue was taken up in MeCN (30 mL) andTMSOTf (0.39 mL, 2.12 mmol) was added. The reaction mixture was heatedat 80° C. for 16 h, cooled to room temperature and concentrated undervacuum. To the residue was added sat. aq. NaHCO₃ (60 mL) and extractedwith EtOAc (3×60 mL). The combined EtOAc layer was washed with water (40mL), brine (30 mL), dried over anhydrous Na₂SO₄, filtered andconcentrated under vacuum. The crude product was purified by silica gelcolumn chromatography (80% EtOAc in petroleum ether) to afford(S)-1-((2R,3S,4S,5R)-5-(2-acetamido-7-(2-(methylthio)ethyl)-6,8-dioxo-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxy-3-fluorotetrahydrofuran-2-yl)propylacetate (76) (200 mg, 27%) as light yellow solid. C₂₁H₂₈FN₅O₈S: ES−, m/z528.1 [M−H]⁻.

Step 6:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(2-(methylthio)ethyl)-7,9-dihydro-1H-purine-6,8-dione(Compound 46)

To a stirred solution of(S)-1-((2R,3S,4S,5R)-5-(2-acetamido-7-(2-(methylthio)ethyl)-6,8-dioxo-1,6,7,8-tetrahydro-9H-purin-9-yl)-4-acetoxy-3-fluorotetrahydrofuran-2-yl)propylacetate (76) (200 mg, 0.37 mmol) in methanol (10 mL), was added K₂CO₃(78.2 mg, 0.56 mmol). The reaction mixture was stirred at roomtemperature for 16 h and concentrated under vacuum to afford a thickpaste. The crude product was purified by Prep-HPLC Column: LUNA OMEGAC18(250*21.2), 5 u Mobile phase: 10 mM ammonium bicarbonate in H₂O:ACNgradient: (T % B): 0/10, 8/55, 10/55, 10.1/98, 13/98, 13.1/10, 16/10.Flow Rate 17 mL/min. Diluent: MeCN+H₂O+THF). Lyophilization of the purefractions afforded2-amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(2-(methylthio)ethyl)-7,9-dihydro-1H-purine-6,8-dione(Compound 46) (45 mg, 29%) as an off-white solid. C₁₅H₂₂FN₅O₅S: ¹H NMR(400 MHz, DMSO-d₆): δ 11.05 (s, 1H), 6.57 (s, 2H), 5.91 (d, J=5.2 Hz,1H), 5.38-5.31 (m, 2H), 5.05-4.90 (m, 1H), 4.85 (d, J=7.2 Hz, 1H), 3.97(t, J=6.8 Hz, 2H) 3.81 (dt, J=22.8, 5.7 Hz, 1H) 3.53 (m, 1H), 2.79 (t,J=6.8 Hz, 2H), 2.10 (s, 3H), 1.48 (m, 1H), 1.33 (m, 1H), 0.91 (t, J=7.4Hz, 3H). ES+, m/z 404.4 [M+H]⁺.

Example 42:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-6-methoxy-7-propyl-7,9-dihydro-8H-purin-8-one,Compound 47

Compound 47 was prepared according to the following multi-stepprocedure.

Step 1: 2-Amino-6-methoxy-9-(4-methoxybenzyl)-7,9-dihydro-8H-purin-8-one(77)

A 30% sodium methoxide solution in MeOH (5.724 mL, 31.8 mmol) was addedto a solution of2-amino-6-chloro-9-(4-methoxybenzyl)-7,9-dihydro-8H-purin-8-one (2) (3g, 7.95 mmol) in MeOH (30 mL) at 0° C. The reaction mixture was warmedto 80° C. and stirred for 16 h. The mixture was then concentrated anddiluted with water (200 mL) and extracted with EtOAc (4×300 mL). Thecombined organic layer was washed with water (100 mL), brine (100 mL),dried over Na₂SO₄, filtered and concentrated under reduced pressure, toafford 2-amino-6-methoxy-9-(4-methoxybenzyl)-7,9-dihydro-8H-purin-8-one(77) (2.5 g, 50%) as an off-white solid. The crude compound was used inthe next step reaction without further purification. C₁₄H₁₅N₅O₃: ¹H NMR(500 MHz, DMSO-d₆): δ 10.79 (brs, 1H), 7.20 (d, J=8.5 Hz, 2H), 6.87 (d,J=8.5 Hz, 2H), 6.25 (s, 2H), 4.78 (s, 2H), 3.87 (s, 3H), 3.71 (s, 3H).ES+, m/z 302.1 [M+H]⁺.

Step 2:2-Amino-6-methoxy-9-(4-methoxybenzyl)-7-propyl-7,9-dihydro-8H-purin-8-one(78)

1-Iodopropane (1.21 mL, 12.43 mmol) was added to a suspension of2-amino-6-methoxy-9-(4-methoxybenzyl)-7,9-dihydro-8H-purin-8-one (77)(2.5 g, 8.305 mmol) and K₂CO₃ (2.5 g, 18.27 mmol) in DMF (25 mL) at 0°C. and stirred at 70° C. for 16 h. To the reaction mixture was added icewater (120 mL) followed by diethyl ether (50 mL) with stirring for 15min. The precipitate that formed was collected by filtration, washedwith water and dried to afford2-amino-6-methoxy-9-(4-methoxybenzyl)-7-propyl-7,9-dihydro-8H-purin-8-one(78) (2.2 g, 78%) as an off-white solid and used as is in the next step.C₁₇H₂₁N₅O₃: ¹H NMR (400 MHz, DMSO-d₆): δ 7.19 (d, J=8.8 Hz, 2H), 6.87(d, J=8.8 Hz, 2H), 6.34 (s, 2H), 4.81 (s, 2H), 3.91 (s, 3H), 3.73-3.68(m, 2H), 3.71 (s, 3H), 1.61 (m, 2H), 0.81 (t, J=7.4 Hz, 3H). ES+, m/z344.2 [M+H]⁺.

Step 3: 2-Amino-6-methoxy-7-propyl-7,9-dihydro-8H-purin-8-one (79)

Trifluoromethanesulfonic acid (1.13 mL, 12.82 mmol) was added to asuspension of2-amino-6-methoxy-9-(4-methoxybenzyl)-7-propyl-7,9-dihydro-8H-purin-8-one(78) (2.2 g, 6.41 mmol) in TFA (0.98 mL, 12.82 mmol) at 0° C. underargon atmosphere and the reaction mixture was slowly warmed to roomtemperature and stirred for 16 h. To the reaction mixture was added icecold water (50 mL) and the pH was made basic with sat. aq. NaHCO₃ (300mL) with vigorous stirring. The residual solid was filtered and takeninto diethyl ether (100 mL), stirred for 30 min, filtered and dried toafford 2-amino-6-methoxy-7-propyl-7,9-dihydro-8H-purin-8-one (79) (1.0g, 70%) as an off-white solid. C₉H₁₃N₅O₂: ¹H NMR (400 MHz, DMSO-d₆): δ11.23 (s, 1H), 6.18 (s, 2H), 3.89 (s, 3H), 3.66 (t, J=6.8 Hz, 2H), 1.60(m, 2H), 0.82 (t, J=7.4 Hz, 3H). ES+, m/z 224.1 [M+H]⁺.

Step 4: N-(6-Methoxy-8-oxo-7-propyl-8,9-dihydro-7H-purin-2-yl)acetamide(80)

Acetic anhydride (1.38 mL, 13.45 mmol) was added to a solution of2-amino-6-methoxy-7-propyl-7,9-dihydro-8H-purin-8-one (79) (1.0 g, 4.48mmol) in AcOH (10 mL) at ambient temperature under argon atmosphere andthe resulting reaction mixture was heated at 120° C. for 4 h. Thereaction mixture was cooled to 0° C. and stirring was continued for 30minutes. The solid product that formed upon cooling was filtered anddried under vacuum to affordN-(6-methoxy-8-oxo-7-propyl-8,9-dihydro-7H-purin-2-yl)acetamide (80)(0.7 g, 63%) as an off-white solid. C₁₁H₁₅N₅O₃: ¹H NMR (400 MHz,DMSO-d₆): δ 11.82 (brs, 1H), 10.22 (s, 1H), 3.99 (s, 3H), 3.74 (t, J=6.8Hz, 2H), 2.17 (s, 3H), 1.63 (m, 2H), 0.83 (t, J=7.4 Hz, 3H). ES+, m/z266.1 [M+H]⁺.

Step 5:(S)-1-((2R,3S,4S,5R)-5-(2-Acetamido-6-methoxy-8-oxo-7-propyl-7,8-dihydro-9H-purin-9-yl)-4-acetoxy-3-fluorotetrahydrofuran-2-yl)propylacetate (81)

N-(6-Methoxy-8-oxo-7-propyl-8,9-dihydro-7H-purin-2-yl)acetamide (80)(200 mg, 0.754 mmol),(3S,4S,5R)-5-((S)-1-acetoxypropyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate (37S) (342 mg, 1.13 mmol) and BSA (0.573 mL, 2.26 mmol) weredissolved in 1,2-dichloroethane (15 mL), and the reaction mixture wasstirred at 80° C. for 30 min under argon. The reaction mixture wascooled to rt, concentrated under vacuum and then taken up inacetonitrile (15 mL). TMSOTf (0.20 mL, 1.13 mmol) was added at rt. andthe reaction mixture was heated at 80° C. for 16 h. The reaction mixturewas concentrated and diluted with water (50 mL) and extracted with EtOAc(3×50 mL). The combined organic layer was washed with brine (50 mL),dried over Na₂SO₄, filtered and concentrated under reduced pressure. Thecrude product was purified by flash column chromatography (SiO₂, 0 to80% EtOAc-pet-ether) to afford(S)-1-((2R,3S,4S,5R)-5-(2-acetamido-6-methoxy-8-oxo-7-propyl-7,8-dihydro-9H-purin-9-yl)-4-acetoxy-3-fluorotetrahydrofuran-2-yl)propylacetate (81) (120 mg, 31%) as an off-white solid. C₂₂H₃₀FN₅O₈. ¹H NMR(400 MHz, DMSO-d₆): δ 10.30 (s, 1H), 6.28 (dd, J=24.0, 5.6 Hz, 1H), 5.67(d, J=5.6 Hz, 1H), 5.36 (dd, J=53.2, 2.8 Hz, 1H), 5.09 (m, 1H), 4.23(dd, J=27.6, 5.2 Hz, 1H), 4.01 (s, 3H), 3.80 (t, J=6.8 Hz, 2H), 2.22 (s,3H), 2.07 (s, 3H), 2.04 (s, 3H), 1.69-1.55 (m, 4H), 0.86 (m, 6H). ES+,m/z 512.6 [M+H]⁺.

Step 6:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-6-methoxy-7-propyl-7,9-dihydro-8H-purin-8-one(Compound 47)

To a solution of(S)-1-((2R,3S,4S,5R)-5-(2-acetamido-6-methoxy-8-oxo-7-propyl-7,8-dihydro-9H-purin-9-yl)-4-acetoxy-3-fluorotetrahydrofuran-2-yl)propylacetate (81) (120 mg, 0.234 mmol) in methanol (5 mL) was added K₂CO₃ (65mg, 0.46 mmol) at 0° C. The reaction mixture was stirred at roomtemperature for 16 h. and applied directly to reverse phase flashchromatography (0.1% HCO₂H:MeCN). Lyophilization of the pure fractionsafforded2-amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-6-methoxy-7-propyl-7,9-dihydro-8H-purin-8-one(Compound 47) (43 mg, 47%) as an off-white solid. C₁₆H₂₄FN₅O₅: ¹H NMR(400 MHz, DMSO-d₆): δ 6.36 (s, 2H), 5.92 (d, J=5.2 Hz, 1H), 5.46 (d,J=7.2 Hz, 1H), 5.42-5.31 (m, 1H), 5.00 (ddd, J=53.4, 4.8, 2.6 Hz, 1H),4.86 (d, J=7.2 Hz, 1H), 3.93 (s, 3H), 3.87-3.81 (m, 1H), 3.73 (t, J=7.0Hz, 2H), 3.53 (m, 1H), 1.63 (m, 2H), 1.49 (m, 1H), 1.34 (m, 1H), 0.91(t, J=7.4 Hz, 3H), 0.85 (t, J=7.4 Hz, 3H). ES+, m/z 386.2 [M+H]⁺.

Example 43:2-Amino-7-butyl-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-6-methoxy-7,9-dihydro-8H-purin-8-one,Compound 48

Compound 48 was prepared according to the following multi-stepprocedure.

Step 1:2-Amino-7-butyl-6-chloro-9-(4-methoxybenzyl)-7,9-dihydro-8H-purin-8-one(82)

1-Bromobutane (3.37 g, 24.59 mmol) was added to a suspension2-amino-6-chloro-9-(4-methoxybenzyl)-7,9-dihydro-8H-purin-8-one (2) (5g, 16.39 mmol), K₂CO₃ (3.39 g, 24.59 mmol) in DMF (50 mL) at 0° C. Thereaction mixture was stirred at room temperature for 24 h, poured in toice cold water and stirred for 30 mins at room temperature. Theprecipitated solid product was collected by filtration and dried undervacuum to afford2-amino-7-butyl-6-chloro-9-(4-methoxybenzyl)-7,9-dihydro-8H-purin-8-one(82) (3 g, 50.6%) as a brown solid. C₁₇H₂₀ClN₅O₂: ¹H NMR (400 MHz,DMSO-d₆): 7.23 (d, J=8.8 Hz, 2H), 6.88 (d, J=8.4 Hz, 2H), 6.73 (s, 2H),4.85 (s, 2H), 3.89 (t, J=7.2 Hz, 2H), 3.72 (s, 3H), 1.62 (m, 2H), 1.31(m, 2H), 0.87 (t, J=7.4 Hz, 3H). ES+, m/z 362.1 [M+H]⁺.

Step 2: 2-Amino-7-butyl-6-chloro-7,9-dihydro-8H-purin-8-one (83)

Trifluoromethane sulphonic acid (2.077 g, 13.85 mmol) was added to astirred solution of2-amino-7-butyl-6-chloro-9-(4-methoxybenzyl)-7,9-dihydro-8H-purin-8-one(82) (2.5 g, 6.92 mmol) in TFA (1.578 g, 13.85 mmol) at 0° C. under anargon atmosphere and the reaction mixture was stirred at RT for 16 h. Tothe mixture was added ice cold water and the pH was made basic with sat.aq. NaHCO₃ while being vigorously stirred. The residual solids werefiltered, taken up in diethyl ether (100 mL) and stirred for 30 min. Thesolids were then filtered and dried to afford2-amino-7-butyl-6-chloro-7,9-dihydro-8H-purin-8-one (83) (1 g; 60%) as abrown solid. C₉H₁₂ClN₅O: ¹H NMR (400 MHz, DMSO-d₆): δ 11.78 (s, 1H),6.56 (s, 2H), 3.82 (t, J=7.2 Hz, 2H), 1.59 (quint, J=7.2 Hz, 2H) 1.29(sext, J=7.4 Hz, 2H) 0.91 (t, J=7.0 Hz, 3H). ES+, m/z 242.1 [M+H]⁺.

Step 3: 2-Amino-7-butyl-6-chloro-7,9-dihydro-8H-purin-8-one (84)

A 30% solution of sodium methoxide in MeOH (2.87 mL, 16.59 mmol) wasadded to a solution of2-amino-7-butyl-6-chloro-7,9-dihydro-8H-purin-8-one (83) (1 g, 4.149mmol) in MeOH (10 mL) at ambient temperature under argon atmosphere. Thereaction mixture was stirred at 90° C. for 16 h, cooled to RT andconcentrated under vacuum. To the crude product was added EtOAc (100 mL)and the organic phase was washed with water (50 mL), brine (2×30 mL),separated, dried over anhydrous Na₂SO₄, and concentrated under vacuum toafford 2-amino-7-butyl-6-methoxy-7,9-dihydro-8H-purin-8-one (84) (200mg, 20.3%) as a yellow solid. C₁₀H₁₅N₅O₂: ¹H NMR (400 MHz, CDCl3): δ10.58 (s, 1H), 6.78 (bs, 2H), 3.98 (s, 3H), 3.89 (t, J=7.2 Hz, 2H),1.71-1.65 (m, 2H), 1.37 (m, 2H), 0.94 (t, J=7.6 Hz, 3H). ES+, m/z 238.1[M+H]⁺.

Step 4: N-(7-Butyl-6-methoxy-8-oxo-8,9-dihydro-7H-purin-2-yl)acetamide(85)

Acetic anhydride (0.2 mL, 1.61 mmol) was added to a solution of2-amino-7-butyl-6-methoxy-7,9-dihydro-8H-purin-8-one (84) (200 mg, 0.81mmol) in acetic acid (5 mL) at ambient temperature under argonatmosphere and the resulting reaction mixture was stirred at 120° C. for3 h. The reaction mixture was cooled to rt and concentrated under vacuumcrude compound was obtained. The crude compound was stirred in diethylether (10 mL) for 30 min. whereupon a solid formed. The product wasfiltered and dried under vacuum to affordN-(7-butyl-6-methoxy-8-oxo-8,9-dihydro-7H-purin-2-yl)acetamide (85) (170mg, 72.3%) as a yellow solid. C₁₂H₁₇N₅O₃: ¹H NMR (400 MHz, DMSO-d₆): δ11.83 (s, 1H), 10.21 (s, 1H), 3.98 (s, 3H), 3.79-3.76 (t, J=7.0 Hz, 2H),2.17 (s, 3H), 1.61 (quint, J=7.2 Hz, 2H), 1.25 (m, 2H), 0.89 (t, J=7.4Hz, 3H). ES+, m/z 280.1 [M+H]⁺.

Step 5:(S)-1-((2R,3S,4S,5R)-5-(2-Acetamido-7-butyl-6-methoxy-8-oxo-7,8-dihydro-9H-purin-9-yl)-4-acetoxy-3-fluorotetrahydrofuran-2-yl)propylacetate (86)

N-(7-Butyl-6-methoxy-8-oxo-8,9-dihydro-7H-purin-2-yl)acetamide (85) (170mg, 0.60 mmol),(3S,4S,5R)-5-((S)-1-acetoxypropyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate (37S) (276 mg, 0.91 mmol) and BSA (369 mg, 1.82 mmol) weredissolved in 1,2-dichloroethane (10 mL) and the resulting reactionmixture was stirred at 80° C. for 30 min. under argon. The reactionmixture was concentrated under reduced pressure and to the residue wasadded MeCN (20 mL) followed by TMSOTf (202 mg, 0.91 mmol). The reactionmixture was heated at 80° C. for 18 h, cooled to room temperature andthe solvent was removed by rotary evaporation. The remaining solids weredissolved in ethyl acetate (50 mL) and extracted with saturated aqueousNaHCO₃ (2×25 mL). The organic phase was dried with Na₂SO₄, filtered andconcentrated. The crude product was purified by GRACE reverse phasechromatography (0.1% HCO₂H in H₂O:MeCN) to afford(S)-1-((2R,3S,4S,5R)-5-(2-acetamido-7-butyl-6-methoxy-8-oxo-7,8-dihydro-9H-purin-9-yl)-4-acetoxy-3-fluorotetrahydrofuran-2-yl)propylacetate (86) (80 mg, 25%) as an yellow solid. C₂₃H₃₂FN₅O₈: ES+, m/z526.2 [M+H]⁺.

Step 6:2-Amino-7-butyl-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-6-methoxy-7,9-dihydro-8H-purin-8-one(Compound 48)

To a solution of(S)-1-((2R,3S,4S,5R)-5-(2-acetamido-7-butyl-6-methoxy-8-oxo-7,8-dihydro-9H-purin-9-yl)-4-acetoxy-3-fluorotetrahydrofuran-2-yl)propylacetate (86) (80 mg, 0.15 mmol) in methanol (5.0 mL) was added K₂CO₃ (42mg, 0.30 mmol) at 0° C. The reaction mixture was stirred at roomtemperature for 16 h. The reaction mixture was applied directly to GRACEreverse phase chromatography (0.1% HCO₂H in H₂O:MeCN) and the purifiedfractions were lyophilized to afford2-amino-7-butyl-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-6-methoxy-7,9-dihydro-8H-purin-8-one(Compound 48) (15 mg, 24.7%), as an off-white solid. C₁₇H₂₆FN₅O₅: ¹H NMR(500 MHz, DMSO-d₆): δ 6.35 (s, 2H), 5.90 (d, J=6.0 Hz, 1H), 5.44 (d,J=7.0 Hz, 1H), 5.40-5.32 (m, 1H), 5.00 (ddd, J=53.5, 4.8, 2.8 Hz, 1H),4.86 (d, J=7.0 Hz, 1H), 3.93 (s, 3H), 3.84 (ddd, J=22.5, 6.5, 5.0 Hz,1H), 3.76 (t, J=7.0 Hz, 2H), 3.53 (m, 1H), 1.59 (m, 2H), 1.48 (m, 1H),1.33 (m, 1H), 1.27 (m, 2H), 0.92-0.88 (m, 6H). ES+, m/z 400.4 [M+H]⁺.

Example 44:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-propyl-7,9-dihydro-1H-purine-6,8-dione,Compound 49

Compound 49 can be prepared according to the procedure in Example 2 with(43) and (14S).

Example 45:2-Amino-7-butyl-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 50

Compound 50 can be prepared according to the procedure in Example 2 with(55) and (14S).

Example 46:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-(2,2,2-trifluoroethyl)-7,9-dihydro-1H-purine-6,8-dione,Compound 51

Compound 51 can be prepared according to the procedure in Example 9 with(72) and (22S).

Example 47:2-Amino-7-(cyclopropylmethyl)-9-((2R,3R,5S)-5-((R)-2-fluoro-1-hydroxyethyl)-3-hydroxytetrahydrofuran-2-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 52

Compound 52 can be prepared according to the procedure in Example 21with (12) and (67S).

Example 48:2-Amino-9-((2R,3R,5S)-5-((R)-2-fluoro-1-hydroxyethyl)-3-hydroxytetrahydrofuran-2-yl)-7-propyl-7,9-dihydro-1H-purine-6,8-dione,Compound 53

Compound 53 can be prepared according to the procedure in Example 21with (43) and (67S).

Example 49:2-Amino-7-butyl-9-((2R,3R,5S)-5-((R)-2-fluoro-1-hydroxyethyl)-3-hydroxytetrahydrofuran-2-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 54

Compound 54 can be prepared according to the procedure in Example 21with (55) and (67S).

Example 50:2-Amino-9-((2R,3R,5S)-5-((R)-2-fluoro-1-hydroxyethyl)-3-hydroxytetrahydrofuran-2-yl)-7-(2,2,2-trifluoroethyl)-7,9-dihydro-1H-purine-6,8-dione,Compound 55

Compound 55 can be prepared according to the procedure in Example 21with (72) and (67S).

Example 51:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-(1-hydroxycyclopropyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 56

Compound 56 can be prepared according to the procedure in Example 16with (6) and(3R,5S)-5-(1-(2,2,2-trifluoroacetoxy)cyclopropyl)tetrahydrofuran-2,3-diyldiacetate.

Example 52:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-(2,2,2-trifluoroacetyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 57

Compound 57 can be prepared from Compound 10 and/or 11.

Example 53:2-Amino-7-(cyclopropylmethyl)-9-((2R,3R,5S)-3-hydroxy-5-(2,2,2-trifluoroacetyl)tetrahydrofuran-2-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 58

Compound 58 can be prepared from Compound 29.

Example 54:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-(2,2,2-trifluoroacetyl)tetrahydrofuran-2-yl)-7-propyl-7,9-dihydro-1H-purine-6,8-dione,Compound 59

Compound 59 can be prepared from Compound 25.

Example 55:2-Amino-7-butyl-9-((2R,3R,5S)-3-hydroxy-5-(2,2,2-trifluoroacetyl)tetrahydrofuran-2-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 60

Compound 60 can be prepared from Compound 31.

Example 56:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-(2,2,2-trifluoroacetyl)tetrahydrofuran-2-yl)-7-(3,3,3-trifluoropropyl)-7,9-dihydro-1H-purine-6,8-dione,Compound 61

Compound 61 can be prepared from Compound 28.

Example 57:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(2-(methylsulfinyl)ethyl)-7,9-dihydro-1H-purine-6,8-dione,Compound 62

Compound 62 can be prepared by the oxidation of Compound 22.

Example 58:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(2-(methylsulfonyl)ethyl)-7,9-dihydro-1H-purine-6,8-dione,Compound 63

Compound 63 can be prepared by the oxidation of Compound 22 or Compound62.

Example 59:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(2-(methylsulfinyl)ethyl)-7,9-dihydro-1H-purine-6,8-dione,Compound 64

Compound 64 can be prepared by the oxidation of Compound 46.

Example 60:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(2-(methylsulfonyl)ethyl)-7,9-dihydro-1H-purine-6,8-dione,Compound 65

Compound 65 can be prepared by the oxidation of Compound 46 or Compound64.

Example 61:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 66

Compound 66 can be prepared according to the procedure in Example 9 with(6) and(3S,4S,5R)-5-(1-(benzoyloxy)-2,2,2-trifluoroethyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate.

Example 62:2-Amino-7-(cyclopropylmethyl)-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 67

Compound 67 can be prepared according to the procedure in Example 26with (12) and(3S,4S,5R)-5-(1-(benzoyloxy)-2,2,2-trifluoroethyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate.

Example 63:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-propyl-7,9-dihydro-1H-purine-6,8-dione,Compound 68

Compound 68 can be prepared according to the procedure in Example 22with (43) and(3S,4S,5R)-5-(1-(benzoyloxy)-2,2,2-trifluoroethyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate.

Example 64:2-Amino-7-butyl-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7,9-dihydro-1H-purine-6,8-dione,Compound 69

Compound 69 can be prepared according to the procedure in Example 28with (55) and(3S,4S,5R)-5-(1-(benzoyloxy)-2,2,2-trifluoroethyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate.

Example 65:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-(2,2,2-trifluoroethyl)-7,9-dihydro-1H-purine-6,8-dione,Compound 70

Compound 70 can be prepared according to the procedure in Example 25with (72) and(3S,4S,5R)-5-(1-(benzoyloxy)-2,2,2-trifluoroethyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate.

Example 66:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-(3,3,3-trifluoropropyl)-7,9-dihydro-1H-purine-6,8-dione,Compound 71

Compound 71 can be prepared according to the procedure in Example 25with (49) and(3S,4S,5R)-5-(1-(benzoyloxy)-2,2,2-trifluoroethyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate.

Example 67:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-((R)-2-hydroxypropyl)-7,9-dihydro-1H-purine-6,8-dione,Compound 72

Compound 72 can be prepared according to the procedure in Example 30with (64) and (37S).

Example 68:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-((S)-2-hydroxypropyl)-7,9-dihydro-1H-purine-6,8-dione,Compound 73

Compound 73 can be prepared according to the procedure in Example 30with (64) and (37S).

Example 69:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-((R)-2-hydroxypropyl)-7,9-dihydro-1H-purine-6,8-dione,Compound 74

Compound 74 can be prepared according to the procedure in Example 9 with(64) and(3S,4S,5R)-5-(1-(benzoyloxy)-2,2,2-trifluoroethyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate.

Example 70:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-((S)-2-hydroxypropyl)-7,9-dihydro-1H-purine-6,8-dione,Compound 75

Compound 75 can be prepared according to the procedure in Example 9 with(64) and(3S,4S,5R)-5-(1-(benzoyloxy)-2,2,2-trifluoroethyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate.

Example 71:(S)-1-((2S,4R,5R)-4-Acetoxy-5-(2-amino-8-oxo-7-(prop-2-yn-1-yl)-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-2-yl)propylacetate, Compound 76

Compound 76 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 6 with acetic anhydride.

Example 72:(S)-1-((2S,4R,5R)-4-Acetoxy-5-(2-amino-7-(cyclopropylmethyl)-8-oxo-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-2-yl)propylacetate, Compound 77

Compound 77 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 5 with acetic anhydride.

Example 73:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-propyl-7,9-dihydro-8H-purin-8-one,Compound 78

Compound 78 can be prepared using the procedure described in Example 5substituting propargyl bromide with 1-iodopropane.

Example 74:(S)-1-((2S,4R,5R)-4-Acetoxy-5-(2-amino-8-oxo-7-propyl-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-2-yl)propylacetate, Compound 79

Compound 79 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 78 with acetic anhydride.

Example 75:2-Amino-7-butyl-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7,9-dihydro-8H-purin-8-one,Compound 80

Compound 80 can be prepared using the procedure described in Example 5substituting propargyl bromide with 1-bromobutane.

Example 76:(S)-1-((2S,4R,5R)-4-Acetoxy-5-(2-amino-7-butyl-8-oxo-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-2-yl)propylacetate, Compound 81

Compound 81 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 80 with acetic anhydride.

Example 77:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(2,2,2-trifluoroethyl)-7,9-dihydro-8H-purin-8-one,Compound 82

Compound 82 can be prepared using the procedure described in Example 5substituting propargyl bromide with 2-bromo-1,1,1-trifluoroethane.

Example 78:(S)-1-((2S,4R,5R)-4-acetoxy-5-(2-amino-8-oxo-7-(2,2,2-trifluoroethyl)-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-2-yl)propylacetate, Compound 83

Compound 83 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 82 with acetic anhydride.

Example 79:(2R,3R,5S)-5-((R)-1-acetoxy-2,2,2-trifluoroethyl)-2-(2-amino-8-oxo-7-(prop-2-yn-1-yl)-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-3-ylacetate, Compound 84

Compound 84 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 36 with acetic anhydride.

Example 80:2-Amino-7-(cyclopropylmethyl)-9-((2R,3R,5S)-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7,9-dihydro-8H-purin-8-one,Compound 85

Compound 85 can be prepared using the procedure described in Example 32and substituting (21) with (14).

Example 81:(2R,3R,5S)-5-((R)-1-Acetoxy-2,2,2-trifluoroethyl)-2-(2-amino-7-(cyclopropylmethyl)-8-oxo-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-3-ylacetate, Compound

Compound 86 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 85 with acetic anhydride.

Example 82:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-propyl-7,9-dihydro-8H-purin-8-one,Compound 87

Compound 87 can be prepared using the procedures described in Examples 5and 32 with (22S) and where propargyl bromide is replaced with1-iodopropane.

Example 83:(2R,3R,5S)-5-((R)-1-Acetoxy-2,2,2-trifluoroethyl)-2-(2-amino-8-oxo-7-propyl-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-3-ylacetate, Compound 88

Compound 88 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 87 with acetic anhydride.

Example 84:2-Amino-7-butyl-9-((2R,3R,5S)-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7,9-dihydro-8H-purin-8-one,Compound 89

Compound 89 can be prepared using the procedures described in Examples 5and 32 with (22S) and where propargyl bromide is replaced with1-bromobutane.

Example 85:(2R,3R,5S)-5-((R)-1-Acetoxy-2,2,2-trifluoroethyl)-2-(2-amino-7-butyl-8-oxo-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-3-ylacetate, Compound 90

Compound 90 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 89 with acetic anhydride.

Example 86:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-(2,2,2-trifluoroethyl)-7,9-dihydro-8H-purin-8-one,Compound 91

Compound 91 can be prepared using the procedures described in Examples 5and 32 with (22S) and where propargyl bromide is replaced with2-bromo-1,1,1-trifluoroethane.

Example 87:(2R,3R,5S)-5-((R)-1-Acetoxy-2,2,2-trifluoroethyl)-2-(2-amino-8-oxo-7-(2,2,2-trifluoroethyl)-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-3-ylacetate, Compound 92

Compound 92 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 91 with acetic anhydride.

Example 88:2-Amino-9-((2R,3R,5S)-5-((R)-2-fluoro-1-hydroxyethyl)-3-hydroxytetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-8H-purin-8-one,Compound 93

Compound 93 can be prepared using the procedures described in Example 5with (21) and (67S).

Example 89:(2R,3R,5S)-5-((R)-1-acetoxy-2-fluoroethyl)-2-(2-amino-8-oxo-7-(prop-2-yn-1-yl)-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-3-ylacetate, Compound 94

Compound 94 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 93 with acetic anhydride.

Example 90:2-Amino-7-(cyclopropylmethyl)-9-((2R,3R,5S)-5-((R)-2-fluoro-1-hydroxyethyl)-3-hydroxytetrahydrofuran-2-yl)-7,9-dihydro-8H-purin-8-one,Compound 95

Compound 95 can be prepared using the procedures described in Example 4with (14) and (67S).

Example 91:(2R,3R,5S)-5-((R)-1-acetoxy-2-fluoroethyl)-2-(2-amino-7-(cyclopropylmethyl)-8-oxo-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-3-ylacetate, Compound 96

Compound 96 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 95 with acetic anhydride.

Example 92:2-Amino-9-((2R,3R,5S)-5-((R)-2-fluoro-1-hydroxyethyl)-3-hydroxytetrahydrofuran-2-yl)-7-propyl-7,9-dihydro-8H-purin-8-one,Compound 97

Compound 97 can be prepared using the procedures described in Examples 5with (67S) where propargyl bromide is replaced with 1-iodopropane.

Example 93:(2R,3R,5S)-5-((R)-1-Acetoxy-2-fluoroethyl)-2-(2-amino-8-oxo-7-propyl-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-3-ylacetate, Compound 98

Compound 98 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 97 with acetic anhydride.

Example 94:2-Amino-7-butyl-9-((2R,3R,5S)-5-((R)-2-fluoro-1-hydroxyethyl)-3-hydroxytetrahydrofuran-2-yl)-7,9-dihydro-8H-purin-8-one,Compound 99

Compound 99 can be prepared using the procedures described in Examples 5with (67S) where propargyl bromide is replaced with 1-bromobutane.

Example 95:(2R,3R,5S)-5-((R)-1-acetoxy-2-fluoroethyl)-2-(2-amino-7-butyl-8-oxo-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-3-ylacetate, Compound 100

Compound 100 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 99 with acetic anhydride.

Example 96:2-Amino-9-((2R,3R,5S)-5-((R)-2-fluoro-1-hydroxyethyl)-3-hydroxytetrahydrofuran-2-yl)-7-(2,2,2-trifluoroethyl)-7,9-dihydro-8H-purin-8-one,Compound 101

Compound 101 can be prepared using the procedures described in Examples5 with (67S) where propargyl bromide is replaced with2-bromo-1,1,1-trifluoroethane.

Example 97:(2R,3R,5S)-5-((R)-1-Acetoxy-2-fluoroethyl)-2-(2-amino-8-oxo-7-(2,2,2-trifluoroethyl)-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-3-ylacetate, Compound 102

Compound 102 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 101 with acetic anhydride.

Example 98:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-(1-hydroxycyclopropyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-8H-purin-8-one,Compound 103

Compound 103 can be prepared according to the procedure in Example 5with (21) and(3R,5S)-5-(1-(2,2,2-trifluoroacetoxy)cyclopropyl)tetrahydrofuran-2,3-diyldiacetate.

Example 99:1-((2S,4R,5R)-4-Acetoxy-5-(2-amino-8-oxo-7-(prop-2-yn-1-yl)-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-2-yl)cyclopropylacetate, Compound 104

Compound 104 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 103 with acetic anhydride.

Example 100:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-(2-hydroxypropan-2-yl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-8H-purin-8-one,Compound 105

Compound 105 can be prepared according to the procedure in Example 5with (21) and (58S).

Example 101:2-((2S,4R,5R)-4-Acetoxy-5-(2-amino-8-oxo-7-(prop-2-yn-1-yl)-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-2-yl)propan-2-ylacetate, Compound 106

Compound 106 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 105 with acetic anhydride.

Example 102:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-(2,2,2-trifluoroacetyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-8H-purin-8-one,Compound 107

Compound 107 can be prepared from Compound 36.

Example 103:2-((2S,4R,5R)-4-Acetoxy-5-(2-amino-8-oxo-7-(prop-2-yn-1-yl)-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-2-yl)propan-2-ylacetate, Compound 108

Compound 108 can be prepared by the O-acetylation of Compound 107 withacetic anhydride.

Example 104:2-Amino-7-(cyclopropylmethyl)-9-((2R,3R,5S)-3-hydroxy-5-(2,2,2-trifluoroacetyl)tetrahydrofuran-2-yl)-7,9-dihydro-8H-purin-8-one,Compound 109

Compound 109 can be prepared from Compound 85.

Example 105:(2R,3R,5S)-2-(2-Amino-7-(cyclopropylmethyl)-8-oxo-7,8-dihydro-9H-purin-9-yl)-5-(2,2,2-trifluoroacetyl)tetrahydrofuran-3-ylacetate, Compound 110

Compound 110 can be prepared by the O-acetylation of Compound 109 withacetic anhydride.

Example 106:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-(2,2,2-trifluoroacetyl)tetrahydrofuran-2-yl)-7-propyl-7,9-dihydro-8H-purin-8-one,Compound 111

Compound 111 can be prepared from Compound 87.

Example 107:(2R,3R,5S)-2-(2-Amino-8-oxo-7-propyl-7,8-dihydro-9H-purin-9-yl)-5-(2,2,2-trifluoroacetyl)tetrahydrofuran-3-ylacetate, Compound 112

Compound 112 can be prepared by the O-acetylation of Compound 111 withacetic anhydride.

Example 108:2-Amino-7-butyl-9-((2R,3R,5S)-3-hydroxy-5-(2,2,2-trifluoroacetyl)tetrahydrofuran-2-yl)-7,9-dihydro-8H-purin-8-one,Compound 113

Compound 113 can be prepared from Compound 89.

Example 109:(2R,3R,5S)-2-(2-Amino-7-butyl-8-oxo-7,8-dihydro-9H-purin-9-yl)-5-(2,2,2-trifluoroacetyl)tetrahydrofuran-3-ylacetate, Compound 114

Compound 114 can be prepared by the O-acetylation of Compound 113 withacetic anhydride.

Example 110:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-(2,2,2-trifluoroacetyl)tetrahydrofuran-2-yl)-7-(2,2,2-trifluoroethyl)-7,9-dihydro-1H-purine-6,8-dione,Compound 115

Compound 115 can be prepared from Compound 51.

Example 111:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-(2,2,2-trifluoroacetyl)tetrahydrofuran-2-yl)-7-(2,2,2-trifluoroethyl)-7,9-dihydro-8H-purin-8-one,Compound 116

Compound 116 can be prepared from Compound 91

Example 112:(2R,3R,5S)-2-(2-Amino-8-oxo-7-(2,2,2-trifluoroethyl)-7,8-dihydro-9H-purin-9-yl)-5-(2,2,2-trifluoroacetyl)tetrahydrofuran-3-ylacetate, Compound 117

Compound 117 can be prepared by the O-acetylation of Compound 116 withacetic anhydride.

Example 113:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-(3,3,3-trifluoropropyl)-7,9-dihydro-8H-purin-8-one,Compound 118

Compound 118 can be prepared using the procedures described in Examples5 and 32 with (22S) and where propargyl bromide is replaced with (46).

Example 114:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-(2,2,2-trifluoroacetyl)tetrahydrofuran-2-yl)-7-(3,3,3-trifluoropropyl)-7,9-dihydro-8H-purin-8-one,Compound 119

Compound 119 can be prepared from Compound 118.

Example 115:(2R,3R,5S)-2-(2-Amino-8-oxo-7-(3,3,3-trifluoropropyl)-7,8-dihydro-9H-purin-9-yl)-5-(2,2,2-trifluoroacetyl)tetrahydrofuran-3-ylacetate, Compound 120

Compound 120 can be prepared by the O-acetylation of Compound 119 withacetic anhydride.

Example 116:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(2-(methylthio)ethyl)-7,9-dihydro-8H-purin-8-one,Compound 121

Compound 121 can be prepared using the procedures described in Example 5with (14S) where propargyl bromide is replaced with(2-chloroethyl)(methyl)sulfane.

Example 117:(S)-1-((2S,4R,5R)-4-acetoxy-5-(2-amino-7-(2-(methylthio)ethyl)-8-oxo-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-2-yl)propylacetate, Compound 122

Compound 122 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 121 with acetic anhydride.

Example 118:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(2-(methylsulfinyl)ethyl)-7,9-dihydro-8H-purin-8-one,Compound 123

Compound 123 can be prepared by the oxidation of 121 with H₂O₂ orm-chloroperbenzoic acid.

Example 119:(1S)-1-((2S,4R,5R)-4-Acetoxy-5-(2-amino-7-(2-(methylsulfinyl)ethyl)-8-oxo-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-2-yl)propylacetate, Compound 124

Compound 124 can be prepared by the oxidation of 122 with H₂O₂ orm-chloroperbenzoic acid.

Example 120:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(2-(methylsulfonyl)ethyl)-7,9-dihydro-8H-purin-8-one,Compound 125

Compound 125 can be prepared by the oxidation of 121 or 123 with H₂O₂ orm-chloroperbenzoic acid.

Example 121:(S)-1-((2S,4R,5R)-4-Acetoxy-5-(2-amino-7-(2-(methylsulfonyl)ethyl)-8-oxo-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-2-yl)propylacetate, Compound 126

Compound 126 can be prepared by the oxidation of 122 or 124 with H₂O₂ orm-chloroperbenzoic acid.

Example 122:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-((R)-2-hydroxypropyl)-7,9-dihydro-8H-purin-8-one,Compound 127

Compound 127 can be prepared using the procedures described in Example 5with (14S) and where propargyl bromide is replaced with(R)-1-bromopropan-2-yl acetate [99457-42-8].

Example 123:(R)-1-(9-((2R,3R,5S)-3-Acetoxy-5-((S)-1-acetoxypropyl)tetrahydrofuran-2-yl)-2-amino-8-oxo-8,9-dihydro-7H-purin-7-yl)propan-2-ylacetate, Compound 128

Compound 128 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 127 with acetic anhydride.

Example 124:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-((S)-2-hydroxypropyl)-7,9-dihydro-8H-purin-8-one,Compound 129

Compound 129 can be prepared using the procedures described in Example 5with (14S) and where propargyl bromide is replaced with(S)-1-bromopropan-2-yl acetate [39968-99-5].

Example 125:(S)-1-(9-((2R,3R,5S)-3-Acetoxy-5-((R)-1-acetoxypropyl)tetrahydrofuran-2-yl)-2-amino-8-oxo-8,9-dihydro-7H-purin-7-yl)propan-2-ylacetate, Compound 130

Compound 130 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 129 with acetic anhydride.

Example 126:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((R)-1-hydroxy-2-(methylthio)ethyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-8H-purin-8-one,Compound 131

Compound 131 can be prepared using the procedures described in Example 5with (21) and (81S).

Example 127:(2R,3R,5S)-5-((R)-1-Acetoxy-2-(methylthio)ethyl)-2-(2-amino-8-oxo-7-(prop-2-yn-1-yl)-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-3-ylacetate, Compound 132

Compound 132 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 131 with acetic anhydride.

Example 128:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxybut-3-yn-1-yl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-8H-purin-8-one,Compound 133

Compound 133 can be prepared using the procedures described in Example 5with (21) and (72S).

Example 129:(S)-1-((2S,4R,5R)-4-Acetoxy-5-(2-amino-8-oxo-7-(prop-2-yn-1-yl)-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-2-yl)but-3-yn-1-ylacetate, Compound 134

Compound 134 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 133 with acetic anhydride.

Example 130:(S)-1-((2R,3S,4S,5R)-4-Acetoxy-5-(2-amino-8-oxo-7-(prop-2-yn-1-yl)-7,8-dihydro-9H-purin-9-yl)-3-fluorotetrahydrofuran-2-yl)propylacetate, Compound 135

Compound 135 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 20 with acetic anhydride.

Example 131:2-Amino-7-(cyclopropylmethyl)-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7,9-dihydro-8H-purin-8-one,Compound 136

Compound 136 can be prepared using the procedures described in Example 4with (14) and (37S).

Example 132:(S)-1-((2R,3S,4S,5R)-4-Acetoxy-5-(2-amino-7-(cyclopropylmethyl)-8-oxo-7,8-dihydro-9H-purin-9-yl)-3-fluorotetrahydrofuran-2-yl)propylacetate, Compound 137

Compound 137 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 136 with acetic anhydride.

Example 133:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-propyl-7,9-dihydro-8H-purin-8-one,Compound 138

Compound 138 can be prepared using the procedures described in Example 5with (37S) and where propargyl bromide is substituted with1-iodopropane.

Example 134:(S)-1-((2R,3S,4S,5R)-4-Acetoxy-5-(2-amino-8-oxo-7-propyl-7,8-dihydro-9H-purin-9-yl)-3-fluorotetrahydrofuran-2-yl)propylacetate, Compound 139

Compound 139 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 138 with acetic anhydride.

Example 135:2-Amino-7-butyl-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7,9-dihydro-8H-purin-8-one,Compound 140

Compound 140 can be prepared using the procedures described in Example 5with (37S) and where propargyl bromide is substituted with1-bromobutane.

Example 136:(S)-1-((2R,3S,4S,5R)-4-Acetoxy-5-(2-amino-7-butyl-8-oxo-7,8-dihydro-9H-purin-9-yl)-3-fluorotetrahydrofuran-2-yl)propylacetate, Compound 141

Compound 141 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 140 with acetic anhydride.

Example 137:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(2,2,2-trifluoroethyl)-7,9-dihydro-8H-purin-8-one,Compound 142

Compound 142 can be prepared using the procedures described in Example 5with (37S) and where propargyl bromide is substituted with2-bromo-1,1,1-trifluoroethane.

Example 138:(S)-1-((2R,3S,4S,5R)-4-Acetoxy-5-(2-amino-8-oxo-7-(2,2,2-trifluoroethyl)-7,8-dihydro-9H-purin-9-yl)-3-fluorotetrahydrofuran-2-yl)propylacetate, Compound 143

Compound 143 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 142 with acetic anhydride.

Example 139:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(3,3,3-trifluoropropyl)-7,9-dihydro-8H-purin-8-one,Compound 144

Compound 144 can be prepared using the procedures described in Example 5with (37S) and where propargyl bromide is substituted with (46).

Example 140:(S)-1-((2R,3S,4S,5R)-4-acetoxy-5-(2-amino-8-oxo-7-(3,3,3-trifluoropropyl)-7,8-dihydro-9H-purin-9-yl)-3-fluorotetrahydrofuran-2-yl)propylacetate, Compound 145

Compound 145 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 144 with acetic anhydride.

Example 141:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(2-(methylthio)ethyl)-7,9-dihydro-8H-purin-8-one,Compound 146

Compound 146 can be prepared using the procedures described in Example 5with (37S) and where propargyl bromide is substituted with(2-chloroethyl)(methyl)sulfane.

Example 142:(S)-1-((2R,3S,4S,5R)-4-acetoxy-5-(2-amino-7-(2-(methylthio)ethyl)-8-oxo-7,8-dihydro-9H-purin-9-yl)-3-fluorotetrahydrofuran-2-yl)propylacetate, Compound 147

Compound 147 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 146 with acetic anhydride.

Example 143:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-8H-purin-8-one,Compound 148

Compound 148 can be prepared using the procedures described in Example 5with (21) and(3S,4S,5R)-5-(1-(benzoyloxy)-2,2,2-trifluoroethyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate.

Example 144:(2R,3S,4S,5R)-5-((R)-1-Acetoxy-2,2,2-trifluoroethyl)-2-(2-amino-8-oxo-7-(prop-2-yn-1-yl)-7,8-dihydro-9H-purin-9-yl)-4-fluorotetrahydrofuran-3-ylacetate, Compound 149

Compound 149 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 148 with acetic anhydride.

Example 145:2-Amino-7-(cyclopropylmethyl)-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7,9-dihydro-8H-purin-8-one,Compound 150

Compound 150 can be prepared using the procedures described in Example 4with (14) and(3S,4S,5R)-5-(1-(benzoyloxy)-2,2,2-trifluoroethyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate.

Example 146:(2R,3S,4S,5R)-5-((R)-1-Acetoxy-2,2,2-trifluoroethyl)-2-(2-amino-7-(cyclopropylmethyl)-8-oxo-7,8-dihydro-9H-purin-9-yl)-4-fluorotetrahydrofuran-3-ylacetate, Compound 151

Compound 151 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 150 with acetic anhydride.

Example 147:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-propyl-7,9-dihydro-8H-purin-8-one,Compound 152

Compound 152 can be prepared using the procedures described in Example 5with(3S,4S,5R)-5-(1-(benzoyloxy)-2,2,2-trifluoroethyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate and where propargyl bromide is substituted with 1-iodopropane.

Example 148:(2R,3S,4S,5R)-5-((R)-1-Acetoxy-2,2,2-trifluoroethyl)-2-(2-amino-8-oxo-7-propyl-7,8-dihydro-9H-purin-9-yl)-4-fluorotetrahydrofuran-3-ylacetate, Compound 153

Compound 153 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 152 with acetic anhydride.

Example 149:2-Amino-7-butyl-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7,9-dihydro-8H-purin-8-one,Compound 154

Compound 154 can be prepared using the procedures described in Example 5with(3S,4S,5R)-5-(1-(benzoyloxy)-2,2,2-trifluoroethyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate and where propargyl bromide is substituted with 1-bromobutane.

Example 150:(2R,3S,4S,5R)-5-((R)-1-Acetoxy-2,2,2-trifluoroethyl)-2-(2-amino-7-butyl-8-oxo-7,8-dihydro-9H-purin-9-yl)-4-fluorotetrahydrofuran-3-ylacetate, Compound 155

Compound 155 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 154 with acetic anhydride.

Example 151:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-(2,2,2-trifluoroethyl)-7,9-dihydro-8H-purin-8-one,Compound 156

Compound 156 can be prepared using the procedures described in Example 5with(3S,4S,5R)-5-(1-(benzoyloxy)-2,2,2-trifluoroethyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate and where propargyl bromide is substituted with2-bromo-1,1,1-trifluoroethane.

Example 152:(2R,3S,4S,5R)-5-((R)-1-acetoxy-2,2,2-trifluoroethyl)-2-(2-amino-8-oxo-7-(2,2,2-trifluoroethyl)-7,8-dihydro-9H-purin-9-yl)-4-fluorotetrahydrofuran-3-ylacetate, Compound 157

Compound 157 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 156 with acetic anhydride.

Example 153:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-(3,3,3-trifluoropropyl)-7,9-dihydro-8H-purin-8-one,Compound 158

Compound 158 can be prepared using the procedures described in Example 5with(3S,4S,5R)-5-(1-(benzoyloxy)-2,2,2-trifluoroethyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate and where propargyl bromide is substituted with (46).

Example 154:(2R,3S,4S,5R)-5-((R)-1-Acetoxy-2,2,2-trifluoroethyl)-2-(2-amino-8-oxo-7-(3,3,3-trifluoropropyl)-7,8-dihydro-9H-purin-9-yl)-4-fluorotetrahydrofuran-3-ylacetate, Compound 159

Compound 159 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 158 with acetic anhydride.

Example 155:(S)-1-((2R,3S,4S,5R)-4-Acetoxy-5-(2-amino-6-methoxy-8-oxo-7-propyl-7,8-dihydro-9H-purin-9-yl)-3-fluorotetrahydrofuran-2-yl)propylacetate, Compound 160

Compound 160 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 47 with acetic anhydride.

Example 156:(S)-1-((2R,3S,4S,5R)-4-Acetoxy-5-(2-amino-7-butyl-6-methoxy-8-oxo-7,8-dihydro-9H-purin-9-yl)-3-fluorotetrahydrofuran-2-yl)propylacetate, Compound 161

Compound 161 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 48 with acetic anhydride.

Example 157:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-6-methoxy-7-(prop-2-yn-1-yl)-7,9-dihydro-8H-purin-8-one,Compound 162

Compound 162 can be prepared using the procedures described in Example43 with (37S) and (2) where 1-bromobutane is replaced with propargylbromide.

Example 158:(S)-1-((2R,3S,4S,5R)-4-Acetoxy-5-(2-amino-6-methoxy-8-oxo-7-(prop-2-yn-1-yl)-7,8-dihydro-9H-purin-9-yl)-3-fluorotetrahydrofuran-2-yl)propylacetate, Compound 163

Compound 163 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 162 with acetic anhydride.

Example 159:2-Amino-7-(cyclopropylmethyl)-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-6-methoxy-7,9-dihydro-8H-purin-8-one,Compound 164

Compound 164 can be prepared using the procedures described in Example42 with (9) and (37S).

Example 160:(S)-1-((2R,3S,4S,5R)-4-Acetoxy-5-(2-amino-7-(cyclopropylmethyl)-6-methoxy-8-oxo-7,8-dihydro-9H-purin-9-yl)-3-fluorotetrahydrofuran-2-yl)propylacetate, Compound 165

Compound 165 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 164 with acetic anhydride.

Example 161:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-6-methoxy-7-(2,2,2-trifluoroethyl)-7,9-dihydro-8H-purin-8-one,Compound 166

Compound 166 can be prepared using the procedures described in Example43 with (37S) and (2) where 1-bromobutane is replaced with2-bromo-1,1,1-trifluoroethane.

Example 162:(S)-1-((2R,3S,4S,5R)-4-Acetoxy-5-(2-amino-6-methoxy-8-oxo-7-(2,2,2-trifluoroethyl)-7,8-dihydro-9H-purin-9-yl)-3-fluorotetrahydrofuran-2-yl)propylacetate, Compound 167

Compound 167 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 166 with acetic anhydride.

Example 163:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-6-methoxy-7-(3,3,3-trifluoropropyl)-7,9-dihydro-8H-purin-8-one,Compound 168

Compound 168 can be prepared using the procedures described in Example43 with (37S) and (2) where 1-bromobutane is replaced with (46).

Example 164:(S)-1-((2R,3S,4S,5R)-4-Acetoxy-5-(2-amino-6-methoxy-8-oxo-7-(3,3,3-trifluoropropyl)-7,8-dihydro-9H-purin-9-yl)-3-fluorotetrahydrofuran-2-yl)propylacetate, Compound 169

Compound 169 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 168 with acetic anhydride.

Example 165:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-6-methoxy-7-(prop-2-yn-1-yl)-7,9-dihydro-8H-purin-8-one,Compound 170

Compound 170 can be prepared using the procedures described in Example43 with (14S) and (2) where 1-bromobutane is replaced with propargylbromide.

Example 166:(S)-1-((2S,4R,5R)-4-Acetoxy-5-(2-amino-6-methoxy-8-oxo-7-(prop-2-yn-1-yl)-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-2-yl)propylacetate, Compound 171

Compound 171 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 170 with acetic anhydride.

Example 167:2-Amino-7-(cyclopropylmethyl)-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-6-methoxy-7,9-dihydro-8H-purin-8-one,Compound 172

Compound 172 can be prepared using the procedures described in Example42 with (9) and (14S).

Example 168:(S)-1-((2S,4R,5R)-4-Acetoxy-5-(2-amino-7-(cyclopropylmethyl)-6-methoxy-8-oxo-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-2-yl)propylacetate, Compound 173

Compound 173 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 172 with acetic anhydride.

Example 169:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-6-methoxy-7-propyl-7,9-dihydro-8H-purin-8-one,Compound 174

Compound 174 can be prepared using the procedures described in Example42 with (14S) and (80).

Example 170:(S)-1-((2S,4R,5R)-4-Acetoxy-5-(2-amino-6-methoxy-8-oxo-7-propyl-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-2-yl)propylacetate, Compound 175

Compound 175 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 174 with acetic anhydride.

Example 171:2-Amino-7-butyl-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-6-methoxy-7,9-dihydro-8H-purin-8-one,Compound 176

Compound 176 can be prepared using the procedures described in Example43 with (14S) and (84).

Example 172:(S)-1-((2S,4R,5R)-4-Acetoxy-5-(2-amino-7-butyl-6-methoxy-8-oxo-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-2-yl)propylacetate, Compound 177

Compound 177 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 176 with acetic anhydride.

Example 173:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-6-methoxy-7-(2,2,2-trifluoroethyl)-7,9-dihydro-8H-purin-8-one,Compound 178

Compound 178 can be prepared using the procedures described in Example43 with (14S) and (2) where 1-bromobutane is replaced with2-bromo-1,1,1-trifluoroethane.

Example 174:(S)-1-((2S,4R,5R)-4-Acetoxy-5-(2-amino-6-methoxy-8-oxo-7-(2,2,2-trifluoroethyl)-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-2-yl)propylacetate, Compound 179

Compound 179 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 178 with acetic anhydride.

Example 175:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-6-methoxy-7-(3,3,3-trifluoropropyl)-7,9-dihydro-8H-purin-8-one,Compound 180

Compound 180 can be prepared using the procedures described in Example43 with (14S) and (2) where 1-bromobutane is replaced with (46).

Example 176:(S)-1-((2S,4R,5R)-4-Acetoxy-5-(2-amino-6-methoxy-8-oxo-7-(3,3,3-trifluoropropyl)-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-2-yl)propylacetate, Compound 181

Compound 181 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 180 with acetic anhydride.

Example 177:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-6-methoxy-7-(prop-2-yn-1-yl)-7,9-dihydro-8H-purin-8-one,Compound 182

Compound 182 can be prepared using the procedures described in Example43 with (22S) and (2) where 1-bromobutane is replaced with propargylbromide.

Example 178:(2R,3R,5S)-5-((R)-1-Acetoxy-2,2,2-trifluoroethyl)-2-(2-amino-6-methoxy-8-oxo-7-(prop-2-yn-1-yl)-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-3-ylacetate, Compound 183

Compound 183 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 182 with acetic anhydride.

Example 179:2-Amino-7-(cyclopropylmethyl)-9-((2R,3R,5S)-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-6-methoxy-7,9-dihydro-8H-purin-8-one,Compound 184

Compound 184 can be prepared using the procedures described in Example42 with (9) and (22S).

Example 180:(2R,3R,5S)-5-((R)-1-Acetoxy-2,2,2-trifluoroethyl)-2-(2-amino-7-(cyclopropylmethyl)-6-methoxy-8-oxo-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-3-ylacetate, Compound 185

Compound 185 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 184 with acetic anhydride.

Example 181:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-6-methoxy-7-propyl-7,9-dihydro-8H-purin-8-one,Compound 186

Compound 186 can be prepared using the procedures described in Example42 with (22S) and (80).

Example 182:(2R,3R,5S)-5-((R)-1-Acetoxy-2,2,2-trifluoroethyl)-2-(2-amino-6-methoxy-8-oxo-7-propyl-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-3-ylacetate, Compound 187

Compound 187 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 186 with acetic anhydride.

Example 183:2-Amino-7-butyl-9-((2R,3R,5S)-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-6-methoxy-7,9-dihydro-8H-purin-8-one,Compound 188

Compound 188 can be prepared using the procedures described in Example43 with (22S) and (84).

Example 184:(2R,3R,5S)-5-((R)-1-Acetoxy-2,2,2-trifluoroethyl)-2-(2-amino-7-butyl-6-methoxy-8-oxo-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-3-ylacetate, Compound 189

Compound 189 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 188 with acetic anhydride.

Example 185:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-6-methoxy-7-(2,2,2-trifluoroethyl)-7,9-dihydro-8H-purin-8-one,Compound 190

Compound 190 can be prepared using the procedures described in Example43 with (22S) and (2) where 1-bromobutane is replaced with2-bromo-1,1,1-trifluoroethane.

Example 186:(2R,3R,5S)-5-((R)-1-Acetoxy-2,2,2-trifluoroethyl)-2-(2-amino-6-methoxy-8-oxo-7-(2,2,2-trifluoroethyl)-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-3-ylacetate, Compound 191

Compound 191 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 190 with acetic anhydride.

Example 187:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-6-methoxy-7-(3,3,3-trifluoropropyl)-7,9-dihydro-8H-purin-8-one,Compound 192

Compound 192 can be prepared using the procedures described in Example43 with (22S) and (2) where 1-bromobutane is replaced with (46).

Example 188:(2R,3R,5S)-5-((R)-1-Acetoxy-2,2,2-trifluoroethyl)-2-(2-amino-6-methoxy-8-oxo-7-(3,3,3-trifluoropropyl)-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-3-ylacetate, Compound 193

Compound 193 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 192 with acetic anhydride.

Example 189:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-6-methoxy-7-(prop-2-yn-1-yl)-7,9-dihydro-8H-purin-8-one,Compound 194

Compound 194 can be prepared using the procedures described in Example43 with(3S,4S,5R)-5-(1-(benzoyloxy)-2,2,2-trifluoroethyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate and (2) where 1-bromobutane is replaced with propargylbromide.

Example 190:(2R,3S,4S,5R)-5-((R)-1-Acetoxy-2,2,2-trifluoroethyl)-2-(2-amino-6-methoxy-8-oxo-7-(prop-2-yn-1-yl)-7,8-dihydro-9H-purin-9-yl)-4-fluorotetrahydrofuran-3-ylacetate, Compound 195

Compound 195 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 194 with acetic anhydride.

Example 191:2-Amino-7-(cyclopropylmethyl)-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-6-methoxy-7,9-dihydro-8H-purin-8-one,Compound 196

Compound 196 can be prepared using the procedures described in Example42 with (9) and(3S,4S,5R)-5-(1-(benzoyloxy)-2,2,2-trifluoroethyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate.

Example 192:(2R,3S,4S,5R)-5-((R)-1-Acetoxy-2,2,2-trifluoroethyl)-2-(2-amino-7-(cyclopropylmethyl)-6-methoxy-8-oxo-7,8-dihydro-9H-purin-9-yl)-4-fluorotetrahydrofuran-3-ylacetate, Compound 197

Compound 197 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 196 with acetic anhydride.

Example 193:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-6-methoxy-7-propyl-7,9-dihydro-8H-purin-8-one,Compound 198

Compound 198 can be prepared using the procedures described in Example42 with(3S,4S,5R)-5-(1-(benzoyloxy)-2,2,2-trifluoroethyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate and (80).

Example 194:(2R,3S,4S,5R)-5-((R)-1-Acetoxy-2,2,2-trifluoroethyl)-2-(2-amino-6-methoxy-8-oxo-7-propyl-7,8-dihydro-9H-purin-9-yl)-4-fluorotetrahydrofuran-3-ylacetate, Compound 199

Compound 199 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 198 with acetic anhydride.

Example 195:2-Amino-7-butyl-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-6-methoxy-7,9-dihydro-8H-purin-8-one,Compound 200

Compound 200 can be prepared using the procedures described in Example43 with(3S,4S,5R)-5-(1-(benzoyloxy)-2,2,2-trifluoroethyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate and (84).

Example 196:(2R,3S,4S,5R)-5-((R)-1-Acetoxy-2,2,2-trifluoroethyl)-2-(2-amino-7-butyl-6-methoxy-8-oxo-7,8-dihydro-9H-purin-9-yl)-4-fluorotetrahydrofuran-3-ylacetate, Compound 201

Compound 201 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 200 with acetic anhydride.

Example 197:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-6-methoxy-7-(2,2,2-trifluoroethyl)-7,9-dihydro-8H-purin-8-one,Compound 202

Compound 202 can be prepared using the procedures described in Example43 with(3S,4S,5R)-5-(1-(benzoyloxy)-2,2,2-trifluoroethyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate and (2) where 1-bromobutane is replaced with2-bromo-1,1,1-trifluoroethane.

Example 198:(2R,3S,4S,5R)-5-((R)-1-Acetoxy-2,2,2-trifluoroethyl)-2-(2-amino-6-methoxy-8-oxo-7-(2,2,2-trifluoroethyl)-7,8-dihydro-9H-purin-9-yl)-4-fluorotetrahydrofuran-3-ylacetate, Compound 203

Compound 203 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 202 with acetic anhydride.

Example 199:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-6-methoxy-7-(3,3,3-trifluoropropyl)-7,9-dihydro-8H-purin-8-one,Compound 204

Compound 204 can be prepared using the procedures described in Example43 with(3S,4S,5R)-5-(1-(benzoyloxy)-2,2,2-trifluoroethyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate and (2) where 1-bromobutane is replaced with (46).

Example 200:(2R,3S,4S,5R)-5-((R)-1-Acetoxy-2,2,2-trifluoroethyl)-2-(2-amino-6-methoxy-8-oxo-7-(3,3,3-trifluoropropyl)-7,8-dihydro-9H-purin-9-yl)-4-fluorotetrahydrofuran-3-ylacetate, Compound 205

Compound 205 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 204 with acetic anhydride.

Example 201:2-Amino-6-chloro-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-8H-purin-8-one,Compound 206

Compound 206 can be prepared using the procedures described in Example43 with (14S) and (2) where 1-bromobutane is replaced with propargylbromide and Step 3 using sodium methoxide is omitted.

Example 202:(S)-1-((2S,4R,5R)-4-acetoxy-5-(2-amino-6-chloro-8-oxo-7-(prop-2-yn-1-yl)-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-2-yl)propylacetate, Compound 207

Compound 207 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 206 with acetic anhydride.

Example 203:2-Amino-6-chloro-7-(cyclopropylmethyl)-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7,9-dihydro-8H-purin-8-one,Compound 208

Compound 208 can be prepared using the procedures described in Example43 with (14S) and (9) where Step 3 using sodium methoxide is omitted.

Example 204:(S)-1-((2S,4R,5R)-4-acetoxy-5-(2-amino-6-chloro-7-(cyclopropylmethyl)-8-oxo-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-2-yl)propylacetate, Compound 209

Compound 209 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 208 with acetic anhydride.

Example 205:2-Amino-6-chloro-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-propyl-7,9-dihydro-8H-purin-8-one,Compound 210

Compound 210 can be prepared using the procedures described in Example43 with (14S) and (2) where 1-bromobutane is replaced with 1-iodopropaneand Step 3 using sodium methoxide is omitted.

Example 206:(S)-1-((2S,4R,5R)-4-Acetoxy-5-(2-amino-6-chloro-8-oxo-7-propyl-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-2-yl)propylacetate, Compound 211

Compound 211 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 210 with acetic anhydride.

Example 207:2-Amino-7-butyl-6-chloro-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7,9-dihydro-8H-purin-8-one,Compound 212

Compound 212 can be prepared using the procedures described in Example43 with (14S) and (83) where Step 3 using sodium methoxide is omitted.

Example 208:(S)-1-((2S,4R,5R)-4-Acetoxy-5-(2-amino-7-butyl-6-chloro-8-oxo-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-2-yl)propylacetate, Compound 213

Compound 213 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 212 with acetic anhydride.

Example 209:2-Amino-6-chloro-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(2,2,2-trifluoroethyl)-7,9-dihydro-8H-purin-8-one,Compound 214

Compound 214 can be prepared using the procedures described in Example43 with (14S) and (2) where 1-bromobutane is replaced with2-bromo-1,1,1-trifluoroethane and Step 3 using sodium methoxide isomitted.

Example 210:(S)-1-((2S,4R,5R)-4-Acetoxy-5-(2-amino-6-chloro-8-oxo-7-(2,2,2-trifluoroethyl)-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-2-yl)propylacetate, Compound 215

Compound 215 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 214 with acetic anhydride.

Example 211:2-Amino-6-chloro-9-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(3,3,3-trifluoropropyl)-7,9-dihydro-8H-purin-8-one,Compound 216

Compound 216 can be prepared using the procedures described in Example43 with (14S) and (2) where 1-bromobutane is replaced with (46) and Step3 using sodium methoxide is omitted.

Example 212:(S)-1-((2S,4R,5R)-4-Acetoxy-5-(2-amino-6-chloro-8-oxo-7-(3,3,3-trifluoropropyl)-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-2-yl)propylacetate, Compound 217

Compound 217 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 216 with acetic anhydride.

Example 213:2-Amino-6-chloro-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-8H-purin-8-one,Compound 218

Compound 218 can be prepared using the procedures described in Example43 with (37S) and (2) where 1-bromobutane is replaced with propargylbromide and Step 3 using sodium methoxide is omitted.

Example 214:(S)-1-((2R,3S,4S,5R)-4-Acetoxy-5-(2-amino-6-chloro-8-oxo-7-(prop-2-yn-1-yl)-7,8-dihydro-9H-purin-9-yl)-3-fluorotetrahydrofuran-2-yl)propylacetate, Compound 219

Compound 219 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 218 with acetic anhydride.

Example 215:2-Amino-6-chloro-7-(cyclopropylmethyl)-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7,9-dihydro-8H-purin-8-one,Compound 220

Compound 220 can be prepared using the procedures described in Example43 with (37S) and (9) where Step 3 using sodium methoxide is omitted.

Example 216:(S)-1-((2R,3S,4S,5R)-4-Acetoxy-5-(2-amino-6-chloro-7-(cyclopropylmethyl)-8-oxo-7,8-dihydro-9H-purin-9-yl)-3-fluorotetrahydrofuran-2-yl)propylacetate, Compound 221

Compound 221 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 220 with acetic anhydride.

Example 217:2-Amino-6-chloro-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-propyl-7,9-dihydro-8H-purin-8-one,Compound 222

Compound 222 can be prepared using the procedures described in Example43 with (37S) and (2) where 1-bromobutane is replaced with 1-iodopropaneand Step 3 using sodium methoxide is omitted.

Example 218:(S)-1-((2R,3S,4S,5R)-4-Acetoxy-5-(2-amino-6-chloro-8-oxo-7-propyl-7,8-dihydro-9H-purin-9-yl)-3-fluorotetrahydrofuran-2-yl)propylacetate, Compound 223

Compound 223 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 222 with acetic anhydride.

Example 219:2-Amino-7-butyl-6-chloro-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7,9-dihydro-8H-purin-8-one,Compound 224

Compound 224 can be prepared using the procedures described in Example43 with (37S) and (83) where Step 3 using sodium methoxide is omitted.

Example 220:(S)-1-((2R,3S,4S,5R)-4-Acetoxy-5-(2-amino-7-butyl-6-chloro-8-oxo-7,8-dihydro-9H-purin-9-yl)-3-fluorotetrahydrofuran-2-yl)propylacetate, Compound 225

Compound 225 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 224 with acetic anhydride.

Example 221:2-Amino-6-chloro-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(2,2,2-trifluoroethyl)-7,9-dihydro-8H-purin-8-one,Compound 226

Compound 226 can be prepared using the procedures described in Example43 with (37S) and (2) where 1-bromobutane is replaced with2-bromo-1,1,1-trifluoroethane and Step 3 using sodium methoxide isomitted.

Example 222:(S)-1-((2R,3S,4S,5R)-4-Acetoxy-5-(2-amino-6-chloro-8-oxo-7-(2,2,2-trifluoroethyl)-7,8-dihydro-9H-purin-9-yl)-3-fluorotetrahydrofuran-2-yl)propylacetate, Compound 227

Compound 227 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 226 with acetic anhydride.

Example 223:2-Amino-6-chloro-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-(3,3,3-trifluoropropyl)-7,9-dihydro-8H-purin-8-one,Compound 228

Compound 228 can be prepared using the procedures described in Example43 with (37S) and (2) where 1-bromobutane is replaced with (46) and Step3 using sodium methoxide is omitted.

Example 224:(S)-1-((2R,3S,4S,5R)-4-Acetoxy-5-(2-amino-6-chloro-8-oxo-7-(3,3,3-trifluoropropyl)-7,8-dihydro-9H-purin-9-yl)-3-fluorotetrahydrofuran-2-yl)propylacetate, Compound 229

Compound 229 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 228 with acetic anhydride.

Example 225:2-Amino-6-chloro-9-((2R,3R,5S)-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-8H-purin-8-one,Compound 230

Compound 230 can be prepared using the procedures described in Example43 with (22S) and (2) where 1-bromobutane is replaced with propargylbromide and Step 3 using sodium methoxide is omitted.

Example 226:(2R,3R,5S)-5-((R)-1-Acetoxy-2,2,2-trifluoroethyl)-2-(2-amino-6-chloro-8-oxo-7-(prop-2-yn-1-yl)-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-3-ylacetate, Compound 231

Compound 231 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 230 with acetic anhydride.

Example 227:2-Amino-6-chloro-7-(cyclopropylmethyl)-9-((2R,3R,5S)-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7,9-dihydro-8H-purin-8-one,Compound 232

Compound 232 can be prepared using the procedures described in Example43 with (22S) and (9) where Step 3 using sodium methoxide is omitted.

Example 228:(2R,3R,5S)-5-((R)-1-Acetoxy-2,2,2-trifluoroethyl)-2-(2-amino-6-chloro-7-(cyclopropylmethyl)-8-oxo-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-3-ylacetate, Compound 233

Compound 233 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 232 with acetic anhydride.

Example 229:2-Amino-6-chloro-9-((2R,3R,5S)-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-propyl-7,9-dihydro-8H-purin-8-one,Compound 234

Compound 234 can be prepared using the procedures described in Example43 with (22S) and (2) where 1-bromobutane is replaced with 1-iodopropaneand Step 3 using sodium methoxide is omitted.

Example 230:(2R,3R,5S)-5-((R)-1-Acetoxy-2,2,2-trifluoroethyl)-2-(2-amino-6-chloro-8-oxo-7-propyl-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-3-ylacetate, Compound 235

Compound 235 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 234 with acetic anhydride.

Example 231:2-Amino-7-butyl-6-chloro-9-((2R,3R,5S)-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7,9-dihydro-8H-purin-8-one,Compound 236

Compound 236 can be prepared using the procedures described in Example43 with (22S) and (83) where Step 3 using sodium methoxide is omitted.

Example 232:(2R,3R,5S)-5-((R)-1-Acetoxy-2,2,2-trifluoroethyl)-2-(2-amino-7-butyl-6-chloro-8-oxo-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-3-ylacetate, Compound 237

Compound 237 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 236 with acetic anhydride.

Example 233:2-Amino-6-chloro-9-((2R,3R,5S)-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-(2,2,2-trifluoroethyl)-7,9-dihydro-8H-purin-8-one,Compound 238

Compound 238 can be prepared using the procedures described in Example43 with (22S) and (2) where 1-bromobutane is replaced with2-bromo-1,1,1-trifluoroethane and Step 3 using sodium methoxide isomitted.

Example 234:(2R,3R,5S)-5-((R)-1-Acetoxy-2,2,2-trifluoroethyl)-2-(2-amino-6-chloro-8-oxo-7-(2,2,2-trifluoroethyl)-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-3-ylacetate, Compound 239

Compound 239 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 238 with acetic anhydride.

Example 235:2-Amino-6-chloro-9-((2R,3R,5S)-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-(3,3,3-trifluoropropyl)-7,9-dihydro-8H-purin-8-one,Compound 240

Compound 240 can be prepared using the procedures described in Example43 with (22S) and (2) where 1-bromobutane is replaced with (46) and Step3 using sodium methoxide is omitted.

Example 236:(2R,3R,5S)-5-((R)-1-Acetoxy-2,2,2-trifluoroethyl)-2-(2-amino-6-chloro-8-oxo-7-(3,3,3-trifluoropropyl)-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-3-ylacetate, Compound 241

Compound 241 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 240 with acetic anhydride.

Example 237:2-Amino-6-chloro-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-8H-purin-8-one,Compound 242

Compound 242 can be prepared using the procedures described in Example43 with(3S,4S,5R)-5-(1-(benzoyloxy)-2,2,2-trifluoroethyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate and (2) where 1-bromobutane is replaced with propargyl bromideand Step 3 using sodium methoxide is omitted.

Example 238:(2R,3S,4S,5R)-5-((R)-1-Acetoxy-2,2,2-trifluoroethyl)-2-(2-amino-6-chloro-8-oxo-7-(prop-2-yn-1-yl)-7,8-dihydro-9H-purin-9-yl)-4-fluorotetrahydrofuran-3-ylacetate, Compound 243

Compound 243 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 242 with acetic anhydride.

Example 239:2-Amino-6-chloro-7-(cyclopropylmethyl)-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7,9-dihydro-8H-purin-8-one,Compound 244

Compound 244 can be prepared using the procedures described in Example43 with(3S,4S,5R)-5-(1-(benzoyloxy)-2,2,2-trifluoroethyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate and (9) where Step 3 using sodium methoxide is omitted.

Example 240:(2R,3S,4S,5R)-5-((R)-1-Acetoxy-2,2,2-trifluoroethyl)-2-(2-amino-6-chloro-7-(cyclopropylmethyl)-8-oxo-7,8-dihydro-9H-purin-9-yl)-4-fluorotetrahydrofuran-3-ylacetate, Compound 245

Compound 245 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 244 with acetic anhydride.

Example 241:2-Amino-6-chloro-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-propyl-7,9-dihydro-8H-purin-8-one,Compound 246

Compound 246 can be prepared using the procedures described in Example43 with(3S,4S,5R)-5-(1-(benzoyloxy)-2,2,2-trifluoroethyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate and (2) where 1-bromobutane is replaced with 1-iodopropane andStep 3 using sodium methoxide is omitted.

Example 242:(2R,3S,4S,5R)-5-((R)-1-Acetoxy-2,2,2-trifluoroethyl)-2-(2-amino-6-chloro-8-oxo-7-propyl-7,8-dihydro-9H-purin-9-yl)-4-fluorotetrahydrofuran-3-ylacetate, Compound 247

Compound 247 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 246 with acetic anhydride.

Example 243:2-Amino-7-butyl-6-chloro-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7,9-dihydro-8H-purin-8-one,Compound 248

Compound 248 can be prepared using the procedures described in Example43 with(3S,4S,5R)-5-(1-(benzoyloxy)-2,2,2-trifluoroethyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate and (83) where Step 3 using sodium methoxide is omitted.

Example 244:(2R,3S,4S,5R)-5-((R)-1-Acetoxy-2,2,2-trifluoroethyl)-2-(2-amino-7-butyl-6-chloro-8-oxo-7,8-dihydro-9H-purin-9-yl)-4-fluorotetrahydrofuran-3-ylacetate, Compound 249

Compound 249 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 248 with acetic anhydride.

Example 245:2-Amino-6-chloro-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-(2,2,2-trifluoroethyl)-7,9-dihydro-8H-purin-8-one,Compound 250

Compound 250 can be prepared using the procedures described in Example43 with(3S,4S,5R)-5-(1-(benzoyloxy)-2,2,2-trifluoroethyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate and (2) where 1-bromobutane is replaced with2-bromo-1,1,1-trifluoroethane and Step 3 using sodium methoxide isomitted.

Example 246:(2R,3S,4S,5R)-5-((R)-1-Acetoxy-2,2,2-trifluoroethyl)-2-(2-amino-6-chloro-8-oxo-7-(2,2,2-trifluoroethyl)-7,8-dihydro-9H-purin-9-yl)-4-fluorotetrahydrofuran-3-ylacetate, Compound 251

Compound 251 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 250 with acetic anhydride.

Example 247:2-Amino-6-chloro-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-(3,3,3-trifluoropropyl)-7,9-dihydro-8H-purin-8-one,Compound 252

Compound 252 can be prepared using the procedures described in Example43 with(3S,4S,5R)-5-(1-(benzoyloxy)-2,2,2-trifluoroethyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate and (2) where 1-bromobutane is replaced with (46) and Step 3using sodium methoxide is omitted.

Example 248:(2R,3S,4S,5R)-5-((R)-1-Acetoxy-2,2,2-trifluoroethyl)-2-(2-amino-6-chloro-8-oxo-7-(3,3,3-trifluoropropyl)-7,8-dihydro-9H-purin-9-yl)-4-fluorotetrahydrofuran-3-ylacetate, Compound 253

Compound 253 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 252 with acetic anhydride.

Example 249:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-((R)-2-hydroxypropyl)-7,9-dihydro-8H-purin-8-one,Compound 254

Compound 254 can be prepared using the procedures described in Example 5with (37S) and where propargyl bromide is replaced with(R)-1-bromopropan-2-yl acetate [99457-42-8].

Example 250:(R)-1-(9-((2R,3S,4S,5R)-3-Acetoxy-5-((S)-1-acetoxypropyl)-4-fluorotetrahydrofuran-2-yl)-2-amino-8-oxo-8,9-dihydro-7H-purin-7-yl)propan-2-ylacetate, Compound 255

Compound 255 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 254 with acetic anhydride.

Example 251:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)-7-((S)-2-hydroxypropyl)-7,9-dihydro-8H-purin-8-one,Compound 256

Compound 256 can be prepared using the procedures described in Example 5with (37S) and where propargyl bromide is replaced with(S)-1-bromopropan-2-yl acetate [39968-99-5].

Example 252:(S)-1-(9-((2R,3S,4S,5R)-3-acetoxy-5-((S)-1-acetoxypropyl)-4-fluorotetrahydrofuran-2-yl)-2-amino-8-oxo-8,9-dihydro-7H-purin-7-yl)propan-2-ylacetate, Compound 257

Compound 257 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 256 with acetic anhydride.

Example 253:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-((R)-2-hydroxypropyl)-7,9-dihydro-8H-purin-8-one,Compound 258

Compound 258 can be prepared using the procedures described in Example 5with (22S) and where propargyl bromide is replaced with(R)-1-bromopropan-2-yl acetate [99457-42-8].

Example 254:(2R,3R,5S)-5-((R)-1-Acetoxy-2,2,2-trifluoroethyl)-2-(7-((R)-2-acetoxypropyl)-2-amino-8-oxo-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-3-ylacetate, Compound 259

Compound 259 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 258 with acetic anhydride.

Example 255:2-Amino-9-((2R,3R,5S)-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-((S)-2-hydroxypropyl)-7,9-dihydro-8H-purin-8-one,Compound 260

Compound 260 can be prepared using the procedures described in Example 5with (22S) and where propargyl bromide is replaced with(S)-1-bromopropan-2-yl acetate [39968-99-5].

Example 256:(2R,3R,5S)-5-((R)-1-Acetoxy-2,2,2-trifluoroethyl)-2-(7-((S)-2-acetoxypropyl)-2-amino-8-oxo-7,8-dihydro-9H-purin-9-yl)tetrahydrofuran-3-ylacetate, Compound 261

Compound 261 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 260 with acetic anhydride.

Example 257:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-((R)-2-hydroxypropyl)-7,9-dihydro-8H-purin-8-one,Compound 262

Compound 262 can be prepared using the procedures described in Example 5with(3S,4S,5R)-5-(1-(benzoyloxy)-2,2,2-trifluoroethyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate and where propargyl bromide is replaced with(R)-1-bromopropan-2-yl acetate [99457-42-8].

Example 258:(2R,3S,4S,5R)-5-((R)-1-acetoxy-2,2,2-trifluoroethyl)-2-(7-((R)-2-acetoxypropyl)-2-amino-8-oxo-7,8-dihydro-9H-purin-9-yl)-4-fluorotetrahydrofuran-3-ylacetate, Compound 263

Compound 263 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 262 with acetic anhydride.

Example 259:2-Amino-9-((2R,3S,4R,5R)-4-fluoro-3-hydroxy-5-((R)-2,2,2-trifluoro-1-hydroxyethyl)tetrahydrofuran-2-yl)-7-((S)-2-hydroxypropyl)-7,9-dihydro-8H-purin-8-one,Compound 264

Compound 264 can be prepared using the procedures described in Example 5with(3S,4S,5R)-5-(1-(benzoyloxy)-2,2,2-trifluoroethyl)-4-fluorotetrahydrofuran-2,3-diyldiacetate and where propargyl bromide is replaced with(S)-1-bromopropan-2-yl acetate [39968-99-5].

Example 260:(2R,3S,4S,5R)-5-((R)-1-Acetoxy-2,2,2-trifluoroethyl)-2-(7-((S)-2-acetoxypropyl)-2-amino-8-oxo-7,8-dihydro-9H-purin-9-yl)-4-fluorotetrahydrofuran-3-ylacetate, Compound 265

Compound 265 can be prepared by the selective mild O-acetylation of thesecondary hydroxyl groups of Compound 264 with acetic anhydride.

Example 1. Activity of Compounds as TLR7 and TLR8 Agonists as Measuredin Reporter Cell Assays

The engagement of TLRs by cognate ligands triggers downstream signalingcascades, leading to the activation of NF-κB and other transcriptionfactors which initiate various immunomodulatory effects. The humanembryonic kidney cell line, HEK293, is essentially non-responsive to TLRagonists, but ectopic expression of TLRs in these cells allows cognateagonists to activate endogenous NF-κB. Accordingly, the HEK293-TLR-NF-κBinducible reporter system is used to assay TLR agonists.

HEK293 cell lines stably expressing human TLR7 or TLR8 together with anNF-κB-driven-secreted alkaline phosphatase (SEAP) reporter were inventedat InvivoGen (San Diego, Calif., USA) and used to assess compounds ofthe present invention for TLR7 and TLR8 agonist activities. Cells wereseeded at 2-5×10⁴ cells/well in 96 well plates (200 μl/well) and treatedwith various concentrations of compound (10 μl) for 15-24 hours. SEAPactivity was determined by measuring OD at 650 nm; the media used toculture the cell lines contains the reagents required for SEAPdetection. The EC₅₀ values in Table 1 are calculated from fitting thedose response of measured SEAP activity for each compound to thefollowing equation: Y=y_(max)*c^(nh)/(EC₅₀ ^(nh)+c^(nh))+blank where Yis the experimentally measured OD₆₅₀ at concentration c of test article,blank is the observed OD₆₅₀ in the absence of TLR7 agonist, y_(max) isthe difference between the measured OD₆₅₀ in the presence of 28.5 μMresiquimod and the blank and values of EC₅₀ and nh are determined bynonlinear least squares analysis. Resiquimod is a known TLR7 and TLR8agonist.

The results of selected compounds tested in TLR7 reporter cells areshown in Table 1. Compound A is5-amino-3-((2R,3R,5S)-3-hydroxy-5-((S)-1-hydroxypropyl)tetrahydrofuran-2-yl)thiazolo[4,5-d]pyrimidine-2,7(3H,6H)-dione)

a known TLR7/TLR8 agonist (International Publication No. WO 2016/146598A1).

TABLE 1 TLR7 Reporter Assay Response at 500 μM Compound as TLR7 ReporterCompound a Percent of Resiquimod Response EC₅₀ (μM) A 74 51 1 67 103 2<5 3 <5 4 81 132 8 <5 9 58 182 10 72 311 11 <5 12 6 >500 μM 13 92 119 14<5 15 <5 16 <5 17 58 358 18 <5 19 <5 22 69 224 23 <5 24 52 327 25 74 32426 59 269 27 61 339 28 47 519 29 79 201 30 87 94 31 78 210 32 68 339 3373 287 34 81 137 35 91 114 37 40 462 38 <5 39 <5 40 <5 41 <5 42 <5 43 9755 44 101 86 45 66 185 46 30 >500 μM

With the exception of Compound A, none of the compounds listed in Table1 displayed significant (>5% of ymax for TLR8 as measured at 28.5 μMresiquimod) activity in a similar TLR8 reporter cell assay atconcentrations up to 500 μM.

Example 2. Induction of Interferon-α and IL6 in hPBMCs (Human PeripheralBlood Mononuclear Cells)

Treatment of hPBMCs with a TLR7 agonist typically induces someproduction of interferon-α as well as lesser amounts of a variety ofother cytokines and chemokines. A typical experiment uses hPBMCsisolated from a healthy donor and placed in replicate cell culturewells; typically 1.0-7.5×10⁶ cells are placed in each well. A testcompound is added and the cells are cultured for 24 hours at 37° C. in ahumidified atmosphere containing 5% CO₂ post-addition; untreatedcontrols are included. Secreted interferon-α production is measuredusing an a multisubtype interferon-α ELISA kit like those from PBL AssaySciences or specifically as IFNα_(2a) as part of a panel of cytokinesand chemokines using luminex methodologies.

The minimal effective concentration (MEC) is the minimum concentrationin a dose response curve where a significant increase in interferon-αproduction (generally at least 80 pg/ml) is observed above baseline. MECvalues for each compound are determined for at least three donors. Theweighted MEC for each compound is the geometric mean of all individualMECs across all donors. Concentrations tested typically consist of atwo-fold dilution series starting at 100 μM. In the calculation ofweighted MEC, any individual MEC value greater the highest concentrationtested is arbitrarily set to two times the highest concentration testedunless all MECs for a compound exceed this value. The maximal amount ofIFNα2a for each donor is determined from dose dependence for eachcompound.

In order to normalize for variation in each hPBMC preparation, thesevalues are first transformed by expressing as a percentage of peakresponse measured with a standard(2-Amino-7-(cyclopropylmethyl)-9-B-D-xylofuranosyl-7,9-dihydro-1H-purine-6,8-dione)and then averaging the results across all donors, this average referredto as IFNrmax. In rare instances, PBMCs from a donor did not producesignificant IFNα2a as defined as >80 pg/ml in response to incubationwith either 50 or 100 μM standard compound while exhibiting substantialproduction in response to the test articles and were omitted fromcalculations of IFNrmax in Table 2 without materially impacting thefindings therein.

When hPBMCs were treated with compounds selected from Table 1, includingCompound A, several induced interferon-α production as shown in Table 2.Compound B is2-Amino-9-((2R,3S,4S,5R)-4-fluoro-3-hydroxy-5-(hydroxymethyl)tetrahydrofuran-2-yl)-7-(prop-2-yn-1-yl)-7,9-dihydro-1H-purine-6,8-dione(U.S. patent application Ser. No. 16/422,050) shown below

TABLE 2 Weighted MEC values from interferon-α production and scaled peakIFNα2a from hPBMCs in-vitro upon incubation with TLR7 agonists. WeightedIFNrmax, Relative Maximal Compound MEC (μM) IFNα2a Production (%) A ≤3.1103 B 17.9 260 1 ≤2.9 316 2 39.7 233 3 >50 ≤10 4 12.5 226 8 5.4 215 96.2 191 10 ≤2.8 283 11 12.5 128 12 15.7 133 13 ≤3.3 353 14 >50 ≤1015 >50 ≤10 16 >50 ≤10 17 ≤3.1 185 18 >50 ≤10 19 >50 ≤10 22 6.3 30723 >50 ≤10 24 12.5 205 25 19.8 80 26 ≤1.6 304 27 ≤1.6 209 28 9.9 105 296.3 83 30 1.6 347 31 6.3 71 32 7.9 223 33 9.9 143 34 1.6 272 35 3.1 20737 79.4 81 38 >50 ≤10 39 >50 ≤10 40 >50 ≤10 41 >50 ≤10 42 >50 ≤10 43 2.5158 44 2.0 250 45 5.0 321 46 3.1 317

A compound is of particular interest if it possesses high potency andhigh IFNα2a production. This combination of features is not typical ofknown TLR7 agonists.

Example 3. MEC and IFN_(max) from Interferon-α Production from hPBMCs inThree Donors

Further insight can be gained by examining the responses in threeindividual donors as shown in Table 3. IFN_(max) is the maximum amountof IFN observed at any concentration across the evaluated concentrationrange. MEC and IFN_(max) values for three select compound are shown forthree donors (Table 3). The range of tested concentrations were 0.625-5μM for Imiquimod, 3.125-100 μM for both Compound A and Compound 1,12.5-100 μM for Compound 2.

TABLE 3 MEC and IFN_(max) values from interferon-α production fromhPBMCs in vitro upon incubation with selected TLR7 agonists in the threeindividual donors*. Donor 1 Donor 2 Donor 3 MEC IFN_(max) MEC IFN_(max)MEC IFN_(max) Compound ID (μM) (pg/ml) (μM) (pg/ml) (μM) (pg/ml)Imiquimod 5  793 5  193 1.25 1350 Compound A ≤3.125 1061 ≤3.125  481≤3.125 2243 Compound 1 ≤3.125 3775 6.25 2129 ≤3.125 5623 Compound 2 504523 >100    9 100 3110 *The amount of IFNα2a product observed in theabsence of TLR7 agonists was <10 pg/ml for all three donors.

Compound 1 possesses a combination of potency (low MEC value) andinterferon production (high IFN_(max) value). Notably, IFN_(max) issubstantially greater for Compound 1 than for the two known TLR7agonists imiquimod and Compound A (4.8-, 11.0- and 4.2-fold for donors1, 2 and 3, respectively for imiquimod; 3.6-, 4.4- and 2.5-fold fordonors 1, 2 and 3, respectively for Compound A). The comparative MECsfor Compound 1 versus 2 are ≤3.125 versus 50 for Donor 1, 6.25 vs>100for Donor 2 and ≤3.125 vs 100 for Donor 3; in every case Compound 1 is≥16-fold more potent than Compound 2.

All references cited herein are incorporated by reference to the sameextent as if each individual publication, database entry (e.g. Genbanksequences or GeneID entries), patent application, or patent, wasspecifically and individually indicated to be incorporated by reference.This statement of incorporation by reference is intended by Applicants,pursuant to 37 C.F.R. § 1.57(b)(1), to relate to each and everyindividual publication, database entry (e.g. Genbank sequences or GeneIDentries), patent application, or patent, each of which is clearlyidentified in compliance with 37 C.F.R. § 1.57(b)(2), even if suchcitation is not immediately adjacent to a dedicated statement ofincorporation by reference. The inclusion of dedicated statements ofincorporation by reference, if any, within the specification does not inany way weaken this general statement of incorporation by reference.Citation of the references herein is not intended as an admission thatthe reference is pertinent prior art, nor does it constitute anyadmission as to the contents or date of these publications or documents.

The present invention is not to be limited in scope by the specificembodiments described herein. Indeed, various modifications of theinvention in addition to those described herein will become apparent tothose skilled in the art from the foregoing description. Suchmodifications are intended to fall within the scope of the appendedclaims.

The foregoing written specification is considered to be sufficient toenable one skilled in the art to practice the invention. Variousmodifications of the invention in addition to those shown and describedherein will become apparent to those skilled in the art from theforegoing description and fall within the scope of the appended claims.

What is claimed is:
 1. A compound having the structure of Formula I:

wherein R¹ is independently —H, —OH, —O—C(O)—R⁸ or —F, R² isindependently —H, —OH, —O—C(O)—R⁸ or —F, R³ is —OH, or —O—C(O)—R⁸, R⁴ is—H, —OH, —O—C(O)—R⁸ or —(C₁-C₈)alkyl, wherein R³ and R⁴ can be in theform of a carbonyl oxygen (═O), R⁵ is —H, —OH, —O—C(O)—R⁸,—(C₁-C₈)alkyl, —O—(C₁-C₈)alkyl, —NH₂ or —NHR⁸ wherein R⁴ and R⁵ can forma 3-6 membered cycloalkyl ring, R⁶ is —H, —(C₁-C₈)alkyl, —C(H)═CH₂,—C(H)═CH(C₁-C₈)alkyl), —C(H)═C(C₁-C₈)alkyl)(C₁-C₈)alkyl), —C(H)═C═CH₂,—C(H)═C═C(C₁-C₈)alkyl)H, —CH₂C≡CH, —OH or —O(C₁-C₈)alkyl, R⁷ is —H, —OH,—OCH₃, —SH or —Cl, R⁸ is independently —(C₁-C₈)alkyl, aryl,—(CH₂)_(n)(aryl), heteroaryl or —(CH₂)_(n)(heteroaryl), n is an integer1, 2, 3, 4 or 5, wherein at least one R⁴ or R⁵ is not —H, wherein eachalkyl, cycloalkyl, aryl and heteroaryl are independently optionallysubstituted by one or more of CN, NO₂, halogen, (C₁-C₃)alkyl,(C₁-C₃)haloalkyl, (C₁-C₃)cycloalkyl, aryl, heteroaryl, OH, alkenyl,alkynyl, O—(C₁-C₃)alkyl, O—C(O)—R⁹, O-(alkylene)aryl,O-(alkylene)heteroaryl, C(O)R⁹, S(C₁-C₈)alkyl, S(O)(C₁-C₈)alkyl,SO₂(C₁-C₈)alkyl, C(O)OR⁹, C(O)NR⁹R⁹, C(O)NR⁹SO₂(C₁-C₈)alkyl, NR⁹R⁹,NR⁹(CO)OR⁹, NH(CO)R⁹, NH(SO₂)(C₁-C₈)alkyl or NH(SO₂)NR⁹R⁹, and R⁹ isindependently —H, —OH, —(C₁-C₈)alkyl, cycloalkyl, heterocyclyl, or thetwo R⁹'s of C(O)NR⁹R⁹ or NR⁹R⁹ combine together with the nitrogen atomto form a heterocycle; or a stereoisomer, a tautomer or apharmaceutically acceptable salt thereof.
 2. The compound of claim 1,wherein R¹ and R² are —H, —OH, or F, or a stereoisomer, a tautomer or apharmaceutically acceptable salt thereof.
 3. The compound of claim 1,wherein R³ is —OH or —O—C(O)—CH₃, or a stereoisomer, a tautomer or apharmaceutically acceptable salt thereof.
 4. The compound of claim 1,wherein R⁴ is —H or —(C₁-C₈)alkyl, or a stereoisomer, a tautomer or apharmaceutically acceptable salt thereof.
 5. The compound of claim 1,wherein R⁴ is —H or —CH₂CH₃, or a stereoisomer, a tautomer or apharmaceutically acceptable salt thereof.
 6. The compound of claim 1,wherein R⁵ is —H or —(C₁-C₈)alkyl, or a stereoisomer, a tautomer or apharmaceutically acceptable salt thereof.
 7. The compound of claim 1,wherein R⁶ is —C(H)═CH₂ or —CH₂C≡CH, or a stereoisomer, a tautomer or apharmaceutically acceptable salt thereof.
 8. The compound of claim 1,wherein R⁷ is —H or —OH, or a stereoisomer, a tautomer or apharmaceutically acceptable salt thereof.
 9. The compound of claim 1,wherein R⁸ is —(C₁-C₈)alkyl, or a stereoisomer, a tautomer or apharmaceutically acceptable salt thereof.
 10. The compound of claim 1,wherein R⁸ is —CH₃, or a stereoisomer, a tautomer or a pharmaceuticallyacceptable salt thereof.
 11. The compound of claim 1, wherein thecompound is selected from the group consisting of:

or a stereoisomer, a tautomer or a pharmaceutically acceptable saltthereof.
 12. A pharmaceutical composition comprising one or morecompounds of claim 1, or a stereoisomer, a tautomer or apharmaceutically acceptable salt thereof, and a pharmaceuticallyacceptable excipient.
 13. A method for treating or preventing aninfectious disease or cancer, the method comprising administering to theindividual an effective amount of one or more compounds of claim 1, or astereoisomer, a tautomer or a pharmaceutically acceptable salt thereof.14. The method of claim 13, wherein the infectious disease is a viralinfection.
 15. The method of claim 14, wherein the viral infection isinfection with a virus selected from the group consisting of HIV,hepatitis virus A, hepatitis virus B, hepatitis virus C, hepatitis virusD, VZV, HSV-I, HAV-6, HSV-II, CMV, Epstein Barr virus, adenovirus,influenza virus, flaviviruses, echovirus, rhinovirus, coxsackie virus,coronavirus, respiratory syncytial virus, mumps virus, rotavirus,measles virus, rubella virus, parvovirus, vaccinia virus, HTLV virus,dengue virus, papillomavirus, molluscum virus, poliovirus, rabies virus,JC virus, arboviral encephalitis virus, SARS-CoV, MERS, and SARS-CoV-2.16. The method of claim 13, wherein the method is for treating orpreventing cancer.
 17. The method of claim 16, wherein the cancer isselected from the group consisting of osteosarcoma, rhabdomyosarcoma,neuroblastoma, kidney cancer, leukemia, renal transitional cell cancer,bladder cancer, Wilm's cancer, ovarian cancer, pancreatic cancer, breastcancer, prostate cancer, bone cancer, lung cancer, non-small cell lungcancer, gastric cancer, colorectal cancer, cervical cancer, synovialsarcoma, head and neck cancer, squamous cell carcinoma, multiplemyeloma, renal cell cancer, retinoblastoma, hepatoblastoma,hepatocellular carcinoma, melanoma, rhabdoid tumor of the kidney,Ewing's sarcoma, chondrosarcoma, brain cancer, glioblastoma, meningioma,pituitary adenoma, vestibular schwannoma, a primitive neuroectodermaltumor, medulloblastoma, astrocytoma, anaplastic astrocytoma,oligodendroglioma, ependymoma, choroid plexus papilloma, polycythemiavera, thrombocythemia, idiopathic myelfibrosis, soft tissue sarcoma,thyroid cancer, endometrial cancer, carcinoid cancer, liver cancer,breast cancer, and gastric cancer.
 18. The method of claim 13 furthercomprising the administration of one or more additional agents, whereinthe one or more agents are each independently an immune checkpointinhibitor, an OX40 agonist, a 4-1BB agonist, an ICOS agonist, a GITRagonist, an IL-2-receptor agonist, or an antibody mediated by ADCC. 19.The method of claim 18, wherein the one or more agents are eachindependently an inhibitor of PD-1, PD-L1, CTLA4, TIM3, LAG3, SIRPα orCD47.
 20. The method of claim 13, further comprising the administrationof one or more additional agents, wherein the one or more additionalagents are each independently a small-molecule therapeutic agent, aprotein or peptide therapeutic, an antibody, sera from persons that haverecovered from a viral infection, or a therapeutic or preventativevaccine.